Peer networking host framework and hosting API

ABSTRACT

A device hosting framework provides hosting for software-implemented logical devices (including peripheral devices bridges) on a computer to expose their services as controlled devices per a peer networking protocol. The device hosting framework encapsulates discovery, description and control protocol operations of the peer networking protocol, which frees the developers of the hosted devices from having to individually implement the peer networking protocol in the hosted devices&#39; software and need implement only the core functionality of the hosted device. The device hosting framework operates as a host supporting device interoperability via the peer networking protocol for multiple hosted devices.

RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 09/872,614,filed Jun. 1, 2001, which in turn claims the benefit of U.S. ProvisionalApplication No. 60/250,863, filed Dec. 1, 2000. Both applications areincorporated herein in their entirety.

TECHNICAL FIELD

This invention relates to peer networking protocols, and moreparticularly relates to host-provided peer networking protocol supportfor hosted devices and software modules.

BACKGROUND AND SUMMARY

A peer networking protocol enables peer-to-peer network connectivityamong networked computing devices. Examples of peer networking protocolsinclude the Universal Plug and Play (UPnP), JINI, HAVI, Salutation, andothers. The UPnP protocol, for example, is designed for pervasivepeer-to-peer network connectivity of PCs of all form factors,intelligent appliances, and wireless devices using a distributed, opennetworking architecture based on TCP/IP and Internet networkingstandards, so as to enable seamless proximity networking in addition tocontrol and data transfer among networked devices in the home, office,and everywhere in between.

Previously in the UPnP protocol, a developer of a logical device(including, without limitation, both hardware devices, such as aportable MP3 audio player hardware, and software devices, such as an MP3audio jukebox software application running on a personal computer) thatwished to expose the device for peer networking via the UPnP protocolwould individually implement the UPnP protocol in that logical device.Additionally, a legacy device built to use a non-UPnP connectivityprotocol (e.g., a personal computer peripheral) could be exposed forpeer networking via UPnP by implementing a “UPnP bridge,” which adaptsbetween the UPnP protocol and the legacy device's non-UPnP connectivityprotocol. In either case, the logical device developer or UPnPbridge-to-legacy device developer would have to expend considerableeffort and work to implement the UPnP protocol in the individual logicaldevice or bridge. Further, where multiple logical devices and/or bridgesexecute using the same hardware computing resources (such as wherelogical devices for the MP3 audio jukebox application and a DVD movieplayer application, together with a UPnP bridge to universal serial bus(USB) peripheral hardware devices, are all running on a same personalcomputer), the separate implementation of the UPnP protocol by each ofthese logical devices and UPnP bridges results in separate consumptionof the computing resources.

The present invention facilitates the development of peer networkingcapable logical devices, eliminating separate and duplicativeimplementation of a peer networking protocol by individual logicaldevices, by providing peer networking hosting of the logical devices. Apeer networking host implements the peer networking protocol andprovides a programming interface for logical devices and bridges toexpose their services to the peer networking protocol using the peernetworking protocol implementation of the host. The logical devices andbridges are thus able to expose their services on the peer networkingprotocol without individually implementing the peer networking protocol.

In accordance with an embodiment of the invention illustrated herein, adevice hosting framework provides services for software and devices on acomputer (hereafter “hosted devices”) to expose themselves as controlleddevices per a peer networking protocol (e.g., the Universal Plug andPlay protocol or another peer networking protocol). The hosted devicescan include bridges to computer peripheral devices and software thatprovide a set of services (e.g., the device's functionality). The devicehosting framework encapsulates discovery, description and controlprotocol operations of the peer networking protocol, which frees thedevelopers of the hosted devices from having to individually implementthe peer networking protocol in the hosted devices' software and needimplement only the core functionality of the hosted device. The devicehosting framework operates as a host supporting device interoperabilityvia the peer networking protocol for multiple hosted devices.

The device hosting framework defines application programming interfaceswith which the hosted devices obtain hosting support for the peernetworking protocol from the device hosting framework. The hosteddevices register with the device hosting framework by providinginformation about their properties. The hosted devices also registerservice objects with the device hosting framework for each service(hereafter “hosted services”) they provide that is to be controllablethrough the peer networking protocol. The service objects individuallyimplement a programming interface (e.g., an IDispatch interface)corresponding to a service description per the peer networking protocolfor the hosted service that it represents. A utility to automaticallygenerate the programming interface from the service description isprovided with the device hosting framework for use by the hosteddevice's developer.

The device hosting framework services discovery and description requestsin the peer networking protocol received from user control point devicesthat are directed to its hosted devices. The device hosting frameworkalso listens for control requests in the peer networking protocol thatare targeted at the hosted devices and services. The device hostingframework translates the control requests into calls to the serviceobjects' programming interfaces (e.g., IDispatch interfaces). The devicehosting framework also translates the return information from theprogramming interface methods into valid control responses in the peernetworking device control protocol.

Additional features and advantages will be made apparent from thefollowing detailed description of the illustrated embodiment whichproceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a peer networking host and hostingapplication programming interface (API) through which hosted logicaldevices expose services for peer networking according to an illustratedembodiment of the invention.

FIG. 2 is a block diagram of a software architecture of the peernetworking host and hosting API of FIG. 1.

FIG. 3 is a block diagram of a translation utility provided by the peernetworking host and hosting API of FIG. 1 for translating a serviceinterface description to an object interface description.

FIG. 4 is a data flow diagram of generating the interfaces of theservice objects of the hosted device in FIG. 2 from the device andservice descriptions.

FIG. 5 is a listing of an illustrative service interface description ina template language.

FIG. 6 is a listing of an illustrative object interface description ininterface definition language produced by the translation utility ofFIG. 3 from the service interface description of FIG. 5.

FIG. 7 is a block diagram of device and service registrar in the peernetworking host and hosting API of FIG. 1.

FIG. 8 is a listing of a registration interface of the registrar of FIG.7.

FIG. 9 is a block diagram of a service control architecture of the peernetworking host of FIG. 1.

FIG. 10 is a block diagram of a web server in the service controlarchitecture of FIG. 7.

FIG. 11 is a listing of a SOAP request structure definition parsed bythe web server of FIG. 10.

FIG. 12 is a listing of a deserialized control request structuredefinition in the web server of FIG. 10.

FIG. 13 is a listing of a control response structure definition in theweb server of FIG. 10.

FIG. 14 is a pseudo-code listing of a deserializer in the web server ofFIG. 10.

FIG. 15 is a listing of a SOAP response structure definition returned bythe web server of FIG. 10.

FIG. 16 is an interface definition language listing of an automationproxy object co-class in the service control architecture of FIG. 9.

FIG. 17 is an interface definition language listing of an eventingmanager object co-class in the software architecture of FIG. 2.

FIG. 18 is an interface definition language listing of an event sourceinterface in the software architecture of FIG. 2.

FIG. 19 is a listing of eventing system data structures in the softwarearchitecture of FIG. 2.

FIG. 20 is a listing of an eventing API in the software architecture ofFIG. 2.

FIG. 21 is a block diagram of an event submission architecture in thepeer networking host and hosting API of FIG. 1.

FIG. 22 is a block diagram of a computer system that may be used to runthe peer networking host and hosting API of FIG. 1.

FIG. 23 is a block diagram of a device having embedded computing andnetworking capability which supports the peer networking host andhosting API of FIG. 1.

FIG. 24 is a block diagram of an exemplary home or office pervasivecomputing environment having a variety of computers as per FIG. 22 andembedded computing devices as per FIG. 23 and incorporating the peernetworking host and hosting API of FIG. 1.

DETAILED DESCRIPTION

In the following detailed description, one implementation of peernetworking hosting according to the invention is embodied in methods,products, and systems that provide a hosting framework and hostingapplication programming interface (herein called the Device Host 100 andthe Device Host API 102 shown in FIG. 1) to support peer networkinginteroperability for hosted devices 108-109 and hosted bridges 110 forbridged devices 112 with other peer networking devices (e.g., UPnPdevices 120-122) over a network 116. The peer networking protocol hostedin the illustrated hosting framework/API implementation may be, forexample, the Universal Plug and Play (UPnP) protocol, which is discussedin more detail in the Appendix section below entitled, “Universal Plugand Play Device Architecture,” or any other peer networking protocol. Inparticular, one implementation of the Device Host 100 and API 102detailed below hosts devices under the UPnP protocol. Alternativeimplementations of the Device Host 100 and API 102 can host devices inother peer networking protocols.

The Device Host API 102 enables software modules (the hosted devices108-109 and bridges 110 for bridged devices 112) to publish themselvesas peer networking-enabled devices. These software modules (includinghosted bridges) are referred to collectively as “hosted devices.” TheDevice Host 100 encapsulates the discovery, description, and controlprotocols of a peer networking protocol, thus requiring hosted devicesto implement only their core functionality.

One implementation detailed below of the Device Host 100 and Host API102 is designed to run on a computing device using the Microsoft Windowsoperating system. Alternative implementations of the Device Host and APIcan be designed for other computing platforms. The illustrated DeviceHost API 102 is particularly targeted to hosted devices 108-110 that arethe hardware computing device itself, bridges to computer peripheralsconnected to the computing device (e.g., universal serial bus (USB)devices, native IEEE 1394 bus devices, native infrared (IRDA) portdevices, computer-enabled cameras, CD-ROM and DVD devices), and “soft”devices running on the computing device (e.g., an MP3 audio jukeboxapplication running on the computing device). Alternative embodimentscan support peer networking hosting for hosted devices that are otherkinds of hardware and/or software-based devices.

The hosted devices 108-110 register themselves with the Device Host 100by providing information about their properties. They also registerservice objects 220 (FIG. 7) with the Device Host for each serviceinstance they contain. The services on hosted devices are referred to ashosted services. Each service object implements a dispatch interface 230corresponding to the Service Description for the service that itrepresents. This dispatch interface is generated automatically from theService Description by a tool.

The Device Host 100 listens for control requests targeted at the hostedservices. It translates these requests into calls to the serviceobjects' dispatch interfaces. It also translates the return informationfrom the methods on the dispatch interfaces into valid controlresponses. The following Device Host Architecture section specifies theparts of the Device Host responsible for receiving control requests,performing these translations, and returning control responses.

The Device Host API 102 includes discovery, description, service controland eventing APIs 130-133, that provide an interface for the hosteddevices and bridges 108-110 to the implementation of those respectivelayers of the peer networking protocol. These APIs are discussed in moredetail in the following sections.

Terminology

In summary, the Device Host of the illustrated embodiment of theinvention uses the following terminology.

-   Device Host The implementation of the Device Host API. The Device    Host is called by hosted services to perform communications with a    network. Functions performed by the Device Host include: processing    control messages, sending event notifications, and sending discovery    announcements and search replies.-   Hosted Service A module written by a client of the Device Host API    that exposes a “service” to the network. A service is able to    receive commands from the network—a Tape Transport service on a VCR,    for example, would allow the network to stop, play, or rewind a    tape.-   Hosted Device A collection of hosted services that perform a logical    function. A “VCR” might be a logical device, comprised of the    “Power”, “Tape Transport” and “Tuner” services.    Device Host Architecture

FIG. 2 illustrates a software architecture (the “Host Architecture”) 140in one implementation of the Device Host 100 (FIG. 1). In the HostArchitecture 140, the Device Host 100 and Host API 102 are implementedin a pair of host executable programs 142, 143 and dynamic link librarymodules 146-148 that are run in the host executable programs' processeson the computing device hardware of the Device Host. A Host DLL 146includes a service Registrar 150, Eventing Managers 153, AutomationProxies 152 and a Web Server 154, which together implement thedescription, service control and eventing APIs 131-133 (FIG. 1) andcorresponding description, service control and eventing operations ofthe Device Host. A Service Discovery API DLL 147 implements thediscovery API 130 (FIG. 1), and communicates via remote procedure calls(RPC) with a Service Discovery Server DLL 148 in the separate hostexecutable program process 143 to provide discovery operations of theDevice Host.

For hosting by the Device Host, the Hosted Devices and Bridges 108-110(FIG. 1) register their services with the Registrar 150 (via a registrarinterface described below), including providing discovery, presentationand control information for their services so that the Device Host canrespond to discovery, presentation and control requests from other peernetworking devices 120-122 for the Hosted Devices and Bridges. In oneimplementation of the Host Architecture 140, Hosted Devices and Bridgesimplemented in any of three ways can be registered with the Registrar150, including as a Device DLL 160 or as a Device Provider DLL 162 runin a container executable process 166, and as a running executableprogram 164. In the Device DLL 160 (e.g., “clientdevice.dll”), thedevices and services can be COM Objects that support a set of interfaces(described below) for integrating with the Device Host. A registeredDevice Provider DLL 162 (e.g., “clientprovider.dll”) implements a deviceprovider (described more fully below) for registering device implementedby other programs. Devices implemented by a separate running executableprogram (e.g., “client.exe”) also can be registered. Any number ofDevice DLLs, Device Provider DLLs, and running Device executables can beregistered. Alternative implementations of the Device Host can supportregistration of other types of programs and structures of HostedDevices.

Once registered, the service discovery API and server DLLs 147, 148provide servicing of discovery requests for the registered services fromother peer networked devices 120-122 (FIG. 1). Also, the Web server 154services incoming requests for description, presentation, servicecontrol and eventing addressed to the registered services from the otherpeer networked devices. The Host Architecture 140 further provides aneventing manager and automation proxy for each registered service tohandle eventing and service control operations under the peer networkingprotocol for the registered services. The eventing manager publishesinformation of the device state to other peer networking devices thathave requested notification under the peer networking protocol. Theautomation proxy receives service control requests under the peernetworking protocol from other peer networking devices via the Webserver, and converts the service control requests to a procedureinvocations of the respective service. Interaction between theregistered hosted device services and the Device Host DLLs generally isaccomplished through COM inter-process procedure calls using a set ofCOM object interfaces described below.

Alternative implementations of the Device Host can be structured withvarious other software architectures, such as with Device Hostoperations and interaction implemented in different configurations ofexecutable programs, library modules, processes, objects, programminginterfaces and procedure calls.

As can be seen from the foregoing discussion of the Host Architecture140, the implementation of the peer networking protocol is provided tohosted devices and services (in Device DLLs, Device Provider DLLs, andDevice executables) by the Device Host 100 (in Host executables 142-143and libraries 146-148). This enables the device/bridge developer toexpose the hosted devices and their services through the peer networkingprotocol by writing the hosted device program as a library or executableto register and interface with the Device Host for hosting by the DeviceHost, and avoid having to fully implement the peer networking protocolindividually in each hosted device.

Further details of the Device Host API 102 (FIG. 1) and the operation ofthe Device Host 100 (FIG. 1) are discussed below. In the followingdiscussion, details specific to an implementation of the Device Host 100for the UPnP protocol on the Microsoft Windows operating systemcomputing platform are described. It should be easily understood thatthese protocol and computing platform-specific details can be readilymodified in alternative implementations of the Device Host to supporthosting of devices and services by the Device Host under other peernetworking protocols on other computing platforms.

Device Host API

The Device Host API 102 (FIG. 1) is a framework that facilitatesimplementing device functionality under a peer networking protocol(e.g., UPnP or other peer networking protocol) on the host computingplatform (e.g., the Microsoft Windows operating system, or othercomputing platform). The Hosted Devices created with the Device Host API102 need only implement their core functionality and can rely on the APIto handle the peer networking protocol-specific details of discovery,description, control, and eventing.

Implementing a Hosted Device

The Device Host API 102 implements the core UPnP protocols: discovery,description, control and eventing. The implementer of a hosted devicemust provide:

-   -   a description of the device and its services    -   an implementation of the device's behavior

For example, the implementer of a clock device provides UPnP device andservice descriptions for the clock device, and an implementation of theclock functions (such as keeping time, setting time, and responding toqueries for the current time). The Device Host API 102 announces thedevice according to the UPnP discovery protocol, responds to queries forthe device's description, routes control requests to the code thatimplements the clock functions, maintains subscriptions, and sends eventnotifications to subscribers when service state changes.

Description

A UPnP device description is an XML document that describes theproperties of a device and the hierarchy of nested devices within it.The schema for UPnP device descriptions, known as the UPnP TemplateLanguage (UTL) for devices, is defined in the Appendix, the UPnP DeviceArchitecture. Device descriptions contain links to service descriptions:separate XML documents that define the list of state variables andactions in a service. Again, the schema for service descriptions, theUPnP Template Language for services, is defined in the UPnP DeviceArchitecture.

The implementer of a hosted device provides device and servicedescriptions for the hosted device. The elements of the devicedescriptions are defined as in the Appendix, the UPnP DeviceArchitecture, with the following exceptions:

-   -   <controlURL>, and <eventSubURL> elements are required by the        Device Host API, and are all empty; the Device Host API fills in        values for these fields when the device is published.    -   <UDN> contains an identifier unique to the device description,        which can be used to lookup the real device UDN generated by the        device host.    -   <SCPDURL> elements do not contain URLs to service descriptions;        rather, contain the service description filename, which is        placed in the resource directory. The setup program of the        device application would determine the location of this        directory.    -   <url> element within the <icon> element do not contain URLs to        device icons; rather, contain the icon filename, which must be        placed in the resource directory.    -   <URLBase> element is not present.        All URLs generated by the Device Host are relative URLs. The        URLs will be relative to the location of the device description        document, sent in the initial device announcement.        Device Behavior Implementation

With reference to FIGS. 3-6, the behavior of a device is defined by theservices it exposes. Each service has a service description 208-209 thatlists its actions and state variables. Together, these comprise theservice interface since they define the ways in which control points caninteract with the service.

To implement a service, a hosted device provides a COM object (the“service object”) 220 that exposes the service's interface 222. In theservice description 208-209, the service interfaces are written in UTL202, but COM object interfaces are typically specified in IDL 204. TheDevice Host API provides a tool 200 that translates a servicedescription 208-209, written as a service description in UTL 202, to aCOM dispinterface description 204, written in IDL.

As an example of this translation, consider FIG. 5: a service interfacedescription written in UTL. The interface translation tool 200, giventhis interface definition, would produce the IDL interface descriptionshown in FIG. 6.

The hosted device 108-110 then implements this dispinterface in order toprovide the functionality of this service. The hosted device implementeruses the translation tool 200 to translate each of the UTL interfaces ofeach service in the device description 206 to an IDL interface, and thenimplement each IDL interface in service objects 220. The objects thatimplement the service dispinterfaces will be referred to as serviceobjects. In case of UPnP errors, the service object would return aDISP_E_EXCEPTION and fill out the EXCEPINFO parameter toIDispatch::Invoke. In particular, the bstrSource field will contain theerror code and bstrDescription will contain the error description.

In addition to implementing the service objects 220, the hosted devicemust implement a device control object 240. The purpose of the devicecontrol object is to serve as a central point of management and controlfor the device's service objects 220. At registration time, the devicecontrol object 240 will be passed to the Device Host API 102, and when acontrol request arrives for one of the device's services, the API willcall into this device control object to ask for the relevant serviceobject. At that time, the device control object can create an instanceof the service object, or return an interface on an already existinginstance.

Device control objects 240 must implement the IUPnPDeviceControlinterface 242, defined below. The Device Host API 102 will call theIUPnPDeviceControl::Initialize( ) method on the device control object,passing it the full text of the UPnP device description it published forthe device, and an initialization string specified at registration time.From this, the device control object can read the UDNs assigned to eachof the devices in the device tree.

When the Device Host API 102 needs a pointer to a service object 220that implements a particular service on the device, it will call theIUPnPDeviceControl::GetServiceObject( ) method on the device controlobject. It passes the UDN and the service ID of the service for which itis requesting a service object, and the address of an IDispatch pointerat which the method is expected to return the service object. Note thatthe UDN parameter is necessary because the device control object managesservices for the entire device tree, including nested devices. Theservice object being requested might be on one of the nested devices;the UDN identifies the device in question.

Registering a Hosted Device

With reference now to FIG. 7, registering a hosted device 108-110 meansproviding the Device Host 100 with the device description 206 (FIG. 4)and its device control object 240 (FIG. 3). The Device Host 100 (FIG. 1)then constructs complete UPnP device descriptions and publish these sothat control points (e.g., at UPnP Devices 120-122 of FIG. 1) can accessthem. The Device Host will then announce the presence of the hosteddevice using UPnP discovery protocols.

Devices can be registered in two ways:

-   -   An application can create an instance of the device control        object 240 (FIG. 3) and pass a pointer to the device control        object to the Device Host API 102 (FIG. 1).    -   The CLSID of a device's control object can be passed to the        Device Host API, which will instantiate the device control        object when needed.

Regardless of which method is used, the Device Host API 102 publishesand announces the device as soon as it is registered. The differencebetween the two approaches has to do with when the device code isloaded: in the first method, the device code is loaded and running atthe time of registration; in the second method, the device code is onlyloaded when a control or event subscription request arrives. Thus, thesecond approach is slightly more optimized, but is not suitable fordevices that need to be running before any control or event subscriptionrequests arrive for them.

Device registration happens through the UPnPRegistrar object 300 of theRegistrar 150 in the Device Host API 102. This object exposes theIUPnPRegistrar interface 302, defined in FIG. 8. To register a devicewith a running device control object 240, an application (e.g., thehosted device application, “client.exe,” 150 of FIG. 2) calls themethod, IUPnPRegistrar::RegisterRunningDevice( ), passing the followingarguments:

-   -   the text of the device's description    -   an IUnknown pointer to the device control object    -   an initialization string that will be passed to the device        control object's IUPnPDeviceControl::Initialize( ) method    -   the location of the resource directory    -   Lifetime of the device    -   Device Identifier out parameter, which is also the return value        of this call.

Registering a device with a device control object that is not runningcan be done either through a command line tool, upnpreg, orprogrammatically, via the IUPnPRegistrar::RegisterDevice( ) method. Thisassumes that the device control object has already been registered withCOM. The command line tool takes the following parameters:

-   -   the name of a file containing the device description    -   the ProgID of the device control object    -   an initialization string that will be passed to the device        control object's IUPnPDeviceControl::Initialize( ) method (this        may be passed in a file)    -   a container identifier: a string that identifies the group to        which the device belongs (all devices with the same container        identifier will be hosted in the same process)    -   Resource path pointing to the location of the service        description and icons    -   Lifetime of the device    -   An optional output file for the device identifier.

To register a non-running device programmatically, an application callsIUPnPRegistrar::RegisterDevice( ) and passes it the following:

-   -   the text of the device's description    -   the ProgID of the device control object    -   an initialization string that will be passed to the device        control object's IUPnPDeviceControl::Initialize( ) method    -   a container identifier    -   the location of the resource directory    -   Device identifier out parameter, which is also the return value        of this call.

Whether registered through the command-line tool, or through theprogrammatic interface, the registrations of non-running devices arepersisted across system reboots in system registry 310. Therefore, oncea device is registered using IUPnPRegistrar::RegisterDevice( ) orupnpreg, it will be published every time the system boots.

A hosted device can be unregistered using the method,IUPnPRegistrar::UnregisterDevice( ), of the UPnP Registrar object 300.This method will remove the hosted device from the Device Host dependingon the value of the fPermanent flag. If this flag is not set, then thedevice will be removed, however it can be re-registered using theIUPnPReregistrar interface. The IUPnPReregistrar::ReregisterDevice( ) orthe IUPnPReregistrar::ReregisterRunningDevice( ) methods using theoriginal root UDN generated by the Device Host and announced on thenetwork. If the flag is not set, then the device will get permanentlydeleted from the Device Host.

Device Providers

Device Providers are registered objects that the system starts on everyreboot. Their purpose is simply to register devices with the Device HostAPI in response to some event.

Device providers are particularly useful for bridging to polled media.Consider, for example, a peripheral device (such as a digital musicplayer) connected to a computer via a serial port. To expose the musicplayer as a UPnP device, a device control object and a set of serviceobjects would be needed to implement the UPnP music player actions asserial commands. But these objects should only be registered once themusic player is plugged into the serial port and available for control.Since the serial port does not offer an explicit notification mechanismfor when devices are connected, some polling code is needed. This codecould be implemented in a device provider object. At system startup, theDevice Host API 102 instantiates the provider object, and tells it tobegin polling. When the Device Host API detected the presence of a musicplayer device, it instantiates the appropriate device control object andregisters it by calling IUPnPRegistrar::RegisterRunningDevice( ). Thiscauses the hosted device to be published and thus exposed to the UPnPnetwork.

The same functionality could be achieved by implementing an NT servicethat polled the serial port. Device providers simplify things byrequiring only the core functionality (the polling) to be implementedsince they rely on the Device Host API to start and stop theirexecution. Thus, all the overhead of implementing an NT service isavoided.

Implementing a Device Provider involves implementing an object thatexposes the IUPnPDeviceProvider interface (defined below). This objectmust be registered with the Device Host API using theIUPnPRegistrar::RegisterDeviceProvider( ) method. This method takesthree arguments:

-   -   a name for the provider (must be unique on the machine)    -   the ProgID of the class that implements the device provider    -   an initialization string    -   a container identifier: a string that identifies the group to        which the device provider belongs (all providers with the same        container identifier will be hosted in the same process)

At registration time (and on every system reboot thereafter), the systeminstantiates the device provider object and calls itsIUPnPDeviceProvider::Start( ) method, passing it the initializationstring specified during registration.

Once the start method has been called, the device provider can do anytype of processing, and when it deems necessary, can register devices bycalling IUPnPRegistrar::RegisterRunningDevice( ), as described in theprevious section.

At system shutdown, the Device Host API calls theIUPnPDeviceProvider::Stop( ) method, to indicate that the deviceprovider should terminate its operations.

Eventing

Every user-defined hosted service object 220 (FIG. 3) implements anumber of standard Device Host interfaces. One of these interfaces isthe IUPnPEventSource interface. This interface implements two methods,namely Advise( ) and Unadvise( ). This provides a mechanism for theDevice Host to subscribe to event notifications generated by the hostedservice.

A hosted service object 220 implements IUPnPEventSource::Advise( ) byquerying the given IUnknown pointer for the IUPnPEventSink interface. Iffound, it then holds a reference to that interface untilIUPnPEventSource::Unadvise( ) is called, or until the hosted serviceobject is deleted. To remove the subscription, the Device Host callsIUPnPEventSource:Unadvise( ) and passes in the same object pointer asfor Advise( ). The hosted service will know to remove the subscriptionif the pointer is the same as the one passed to Advise( ).

When the hosted service wishes to notify the Device Host 100 (FIG. 1)that an event has occurred, it can then call theIUPnPEventSink::OnStateChanged( ) method to do so.

When the Device Host no longer wishes to receive notifications from thehosted service, it will call IUPnPEventSource::Unadvise( ), passing inthe same object pointer that it received in theIUPnPEventSource::Advise( ) call.

Service Control API

With reference now to FIG. 9, the service control API 132 (FIG. 1) inthe Device Host API implements the UPnP control protocol, which isdescribed in more detail in the Appendix, “Universal Plug and PlayDevice Architecture.” Specifically, the service control API isresponsible for

-   -   decoding UPnP control requests from the network    -   routing the requests to the hosted device code that executes        them    -   generating UPnP control responses

The service control API 132 isolates all the UPnP protocol specificprocessing from the hosted device code, making control requests looklike simple method calls. FIG. 9 shows a control system softwarearchitecture 400 of the service control API of the Device Host 100.

Two main components form the core of the control system softwarearchitecture 400:

-   -   a Web Server 154 that handles the exchange and processing of        control messages    -   an Automation Proxy 152 that calls into a hosted devices'        service objects 220 to execute control requests        Web Server

All UPnP control messages travel over HTTP and the Device Host API 102(FIG. 1) includes the Web Server 154 (FIG. 2) as its HTTP server forHTTP requests/responses.

The Device Host API 102 (FIG. 1) sets up the control URLs of hosteddevices 108-110 to point to the Web Server 154. When the Web Serverreceives an HTTP request with one of the hosted devices' control URLs,the Web Server verifies that the HTTP packet contains a control request,parses the contents of the request, and invokes the Automation Proxy forthe service to cause the service to execute the control request. Whenthe hosted device code returns, the Web Server forms a UPnP controlresponse, and sends this back to the originator of the request overHTTP.

FIG. 10 illustrates the internals of the Web Server 154. Controlrequests pass through the following components:

-   -   SOAP Parser 440: loads the SOAP XML text from the body of the        HTTP message and parses it into a stream of tokens.    -   Deserializer 450: decodes each SOAP token, converting from text        to binary form using the UPnP type information for state        variables and arguments.

The deserializer 450 makes use of an automation proxy object 152 (FIG.9) that provides the data type information required to translate data inthe SOAP requests into the binary form required by the serviceimplementations. Once translated, the automation proxy object 152forwards the request to the hosted device code, by calling into itsservice objects 220 (FIG. 9).

When the call completes, the automation proxy object 152 passes thereturn information (return value and the values of any output arguments)to the Web Server 154. This information passes through the followingcomponents:

-   -   Serializer 460 (FIG. 10): converts the binary return value and        argument data into text form using UPnP type information and        forms a stream of SOAP tokens.    -   SOAP Generator 470 (FIG. 10): forms the XML text of a SOAP        response and returns this to the originator of the request

The following sections discuss further details of implementation of theillustrated Web Server.

Identifying Service Instances

The same Web Server 154 will receive control requests for all hosteddevices on a particular machine and therefore all control URLs willpoint to this extension. In order to make each service's control URLunique, it will include a unique query string. Thus control URLs are ofthe following form:

-   -   http://<virtual directory path>/web-server-api.dll?<unique        identifier>        <virtual directory path> is the path to the virtual directory in        which the Web Server is located. <unique identifier> is a        concatenation of:    -   the UDN of the hosted device to which the service belongs    -   the service ID    -   a short string that is randomly generated at publication time

This unique identifier is referred to as the service instance name. Therandomly generated string in the service instance name ensures that thecontrol URLs for the services on the hosted device are different eachtime the device is published). The following is an example of a completecontrol URL for a hosted service:

-   -   http://server1/upnphost/web-server-api.dll?uuid:debe205c-b2d8-4886-b60f-3898841a3f41:urn:upnp-org:serviceId:myService:745232

Given the service instance name in the control URL, the Web Server 154is able to locate the service implementation in the hosted device. To dothis, the Web Server instantiates the Registrar 150 (FIG. 7) and queriesfor the IUPnPRegistrar interface. Since the UPnP registrar is thecentral repository of information about running devices, it is able tolocate the service implementation in the hosted device. The Web Servercalls IUPnPRegistrar::GetAutomationProxy( ), passing it the serviceinstance name. This method returns the IUPnPAutomationProxy interface onthe automation proxy object 152 bound to the service implementation. TheWeb Server can use this automation proxy object to obtain typeinformation from the service description, or to invoke control requestson the service object.

Parsing SOAP Requests

The bodies of control requests contain XML encoded according to the SOAPrules. In processing a control request, the first task of the SOAPparser 440 is to read the entire request body sent by the client (e.g.,UPnP Devices 120-122 of FIG. 1), since the extension control block maynot contain all of the request. The SOAP parser examines thecbTotalBytes field in the extension control block, and if its value isgreater than the value in the cbAvailable field, the SOAP parser readsthe remaining data using the ReadClient( ) Web Server callback function.

Once the data has been read, the SOAP parser converts the request fromsingle-byte to wide characters, creates an XML DOM document object andloads the text into the document object. The SOAP parser then validatesthat the essential SOAP elements are present and correctly formed, andextracts the data pertinent to the request. Specifically, the SOAPparser creates an instance of the UPNP_SOAP_REQUEST structure shown inFIG. 11 and populate the structure's fields by walking the XML DOM nodetree created from the request text.

With reference to FIG. 11, the bstrActionName field in theUPNP_SOAP_REQUEST structure contains the name of the action, extractedfrom the name of the first child of the SOAP Body element. The pxndlArgsfield contains a list of XML nodes that represent the action'sarguments. These nodes contain the name of the arguments and theirvalues, represented in text form. This structure is passed to thedeserializer 450, which converts the argument values from text to theirappropriate binary representations.

Deserializing SOAP Requests

Using the type information from the UPnP Service Description for thetarget service, the deserializer 450 can convert the arguments in aUPNP_SOAP_REQUEST structure into their binary form. The deserializer 450places the deserialized values into a UPNP_CONTROL_REQUEST structure, asdefined in FIG. 12.

The deserializer takes the following arguments:

-   -   a pointer to the UPNP_SOAP_REQUEST structure (FIG. 11) produced        by the SOAP Parser.    -   a pointer to the IUPnPServiceDescriptionInfo interface on the        automation proxy object 152.    -   a pointer to a UPNP_CONTROL_REQUEST structure (FIG. 12) in which        to place the deserialized argument values.

FIG. 14 shows pseudo-code for the deserializer 450. The deserializerbegins by setting up the UPNP_CONTROL_REQUEST structure (copying theaction name and allocating space for the array of VARIANT arguments).The deserializer then walks through the list of argument nodes in theUPNP_SOAP_REQUEST structure, sets the data type on each one according tothe type information obtained from the IUPnPServiceDescriptionInfointerface on the automation proxy object 152, and then extracts thetyped value. The result is a UPNP_CONTROL_REQUEST structure containingan array of VARIANTs with the typed values for each of the actionarguments.

The deserialized request data is then passed to the automation proxyobject 152 that invokes the appropriate method on the service object 220to fulfill the request. The automation proxy returns with deserializedreturn information in a UPNP_CONTROL_RESPONSE structure (defined in FIG.13). This structure contains an anonymous union, overlaying the returninformation for success and failure responses. The HRESULT returned bythe automation proxy object 152 determines which set of informationshould be examined. This information is passed to the Serializer 460(FIG. 10) before being encapsulated into a SOAP response.

Serializing Control Responses

The serializer 460 (FIG. 10) converts the binary representations of thereturn values and output arguments returned by the automation proxyobject 152 (FIG. 9) into text XML form. The serializer does this byconsulting the argument type information from the UPnP ServiceDescription and using the XML DOM to encode the data appropriately. Theserializer 460 produces an instance of the UPNP_SOAP_RESPONSE structure,defined in FIG. 15.

For success responses, the serializer 460 will convert the binaryVARIANT representations of the output arguments and return value intoXML nodes. The names of the output arguments will be obtained from theIUPnPServiceDescriptionInfo interface on the automation proxy object.For failure responses, the serializer 460 simply converts the UPnP errorcode into a string.

Generating SOAP Responses

The SOAP Generator 470 (FIG. 10) forms the XML text of a SOAP responsebased on the UPNP_SOAP_RESPONSE structure built by the serializer 460,and returns this to the originator of the request.

Automation Proxy

With reference again to FIG. 9, incoming UPnP control requests followthe UPnP control protocol rules for encoding and message exchange.Service implementations in hosted devices follow the COM Automationrules for method invocation. Automation proxy objects 152 (FIG. 9) serveas the interface between the UPnP control protocol and COM Automation.Automation proxy objects take UPnP action names and deserializedarguments, and make calls to the dispinterfaces on service objects 220.In addition, automation proxy objects map data types of service statevariables and action arguments, as declared in the UPnP servicedescription, to COM automation data types.

The Device Host API 102 instantiates one automation proxy object 152 perservice object 220.

Binding to a Service Object

The Device Host API 102 (FIG. 1) obtains service objects 220 by callinginto the device control objects 240 (FIG. 3) of hosted devices.Specifically, the Device Host API calls theIUPnPDeviceControl::GetServiceObject( ) method to obtain an IDispatchinterface on an object that implements a particular service.

The first time the API 102 gets a service object 220, it instantiates anautomation proxy object 152 to be bound to it. In the binding operation,the Device Host 100 passes the service object's IUnknown pointer and thetext of the service description to an initialization function on theautomation proxy object 152. Thereafter, the newly created automationproxy object 152 handles all incoming control requests to the serviceobject.

Parsing the Service Description

During its initialization, the automation proxy object 152 parses theservice description and build two internal tables: one that stores thedata types of service state variables, and another that stores the datatypes of the arguments to the service's actions. These tables will thenserve as the source for the data type information the automation proxyreturns through its IUPnPServiceDescriptionInfo interface (defined inAppendix, “UPnP Device Host API Reference”). Note that these tablesstore only the names and data types, not values, of the state variablesand arguments.

Threading Model

Automation proxy objects 152 (FIG. 9) keep no state and, after settingup data type tables at initialization time, are completely read-only.Thus, any number of threads can call methods on an automation proxyobject concurrently and no explicit synchronization is required. Theautomation proxy object is free-threaded.

CoClass

Automation proxy objects will be instances of the UPnPAutomationProxycoclass defined in the interface definition language description of FIG.16.

Eventing API

With reference again to FIG. 1, the Eventing API 133 allows hosteddevices/bridges 108-110 to notify interested UPnP Devices 120-122 on theUPnP network 116 of changes to their state.

The eventing API 133 relieves the hosted devices/bridges of having towrite a UPnP/GENA eventing server, including accepting and maintainingclient event subscriptions and generating UPnP event messages.Additionally, the Eventing API provides automatic moderation for certaintypes of moderated events.

Eventing Manager Object

In the software architecture 140 (FIG. 2) of the Device Host 100, theeventing API 133 is implemented using an eventing manager object 153.The eventing manager (EM) object 153 manages subscription informationfor each service hosted by a device and handles submission of events forthat service. If not already created, the EM object 153 is created bythe Registrar object 150 when a SUBSCRIBE request is received.

The Registrar 150 is passed the UDN and service identifier for aspecific service and returns the EM object. Eventing manager objectsexport the IUPnPEventingManager and IUPnPEventSink interfaces defined inFIG. 17.

Implementation

The EM object 153 is a light wrapper around the lower-level eventingAPI. All of the methods of both the IUPnPEventingManager andIUPnPEventSink interfaces effect a call to one of the low-level eventingAPIs. Since the wrapper object is COM-based, the Web Server has theability to communicate with the central host service from its ownprocess. The methods are implemented as follows:

IUPnPEventingManager

The Initialize( ) method of the IUPnPEventingManager interface connectsthe EM object 153 with the hosted service object 220 supplied by thedevice writer and the automation proxy 152 (FIG. 9) for that service. Italso communicates the UDN and service identifier of the device andservice for which it is handling eventing. Inside the Initialize( )method, the EM object queries the hosted service object 220 it waspassed for the IUPnPEventSource interface. It will then callIUPnPEventSource::Advise( ) and pass its own outgoing interface(IUPnPEventSink) to the hosted service object. When the hosted serviceobject wishes to submit an event, it will call the OnStateChanged( )method on this interface. The EM object would then query the serviceobject for the state variable names, their new values, and their types,and internally call the HrSubmitEvent( ) API.

AddSubscriber( ) does the following:

-   -   It queries the automation proxy object for the names, values,        and types of ALL state variables for the particular service.    -   Using this information, the function creates an XML DOM Document        and extracts the XML from the document as a string    -   It calls the low-level HrAddSubscriber( ) API for the related        event source, passing in the Callback URL from the SUBSCRIBE        message, the timeout, and the newly created body.    -   Upon return, HrAddSubscriber( ) provides the SID of the new        subscription and the timeout chosen so that the caller can send        the appropriate response. AddSubscriber( ) returns this SID as        well.

The RenewSubscriber( ) method takes the SID and timeout from theSUBSCRIBE request and renews the corresponding subscription. Upon returnthe timeout parameter receives the value chosen by the Device Host.

The RemoveSubscriber( ) method takes the SID from the UNSUBSCRIBErequest and removes the corresponding subscriber from the list.

The Shutdown( ) method balances out the Initialize( ) method by simplycalling Unadvise( ) on the IUPnPEventSource interface it has.

IUPnPEventSink

The IUPnPEventSink::OnStateChanged( ) method of the IUPnPEventSinkinterface is called by the hosted service object 220 to notify the EMobject 153 that its state has changed. This method is hidden from VBusers since they should use the OnStateChangedSafe( ) method instead.The EM object then does the following:

-   -   Query the automation proxy object to get the names, values, and        types for each DISPID passed to OnStateChanged( ).    -   Then build an XML DOM Document using this information.    -   Extract the XML string from the DOM    -   Internally call the HrSubmitEvent( ) API with the saved event        source identifier and the newly created body.

The IUPnEventSink::OnStateChangedSafe( ) method is intended for use byVB programmers so that they may communicate the names and values ofvariables that have changed to the Device Host. C++ programmers may callthis method as well, but it is not expected that they will do so sinceit requires considerably more work.

User-Implemented Eventing Interfaces

Every user-defined hosted service object 220 will implement a number ofstandard Device Host interfaces. One of these interfaces is theIUPnPEventSource interface. This interface implements two methods,namely Advise( ) and Unadvise( ). This provides a mechanism for thecorresponding Eventing Manager object to subscribe to eventnotifications generated by the hosted service. This interface is definedin FIG. 18.

Implementing IUPnPEventSource

A hosted service will implement the IUPnPEventSource::Advise( ) methodby querying the given IUnknown pointer for the IUPnPEventSink interface.If found, it would then hold a reference to that interface untilIUPnPEventSource::Unadvise( ) is called, or until the hosted serviceobject is deleted. To remove the subscription, the EM object 153 callsIUPnPEventSource:Unadvise( ) and passes in the same object pointer asfor Advise( ). The hosted service knows to remove the subscription ifthe pointer is the same as the one passed to Advise( ).

When the hosted service wishes to notify the Device Host that an eventhas occurred, it can then call the IUPnPEventSink::OnStateChanged( )method to do so.

When the Device Host no longer wishes to receive notifications from thehosted service, it calls IUPnPEventSource::Unadvise( ), passing in apointer to its own IUnknown interface; the same interface it passed tothe Advise( ) call.

Low-Level Eventing API

A low-level eventing API defined in FIG. 20 is a private interfacebetween the EM object 153 and the central UPnP host service. It is ahighly scalable API that is called for all hosted services on thecomputer.

Event Source Identifier

All of the low-level eventing API functions require the event sourcesidentifier as the first parameter. The reason for this is to ensure thatevery function operates on a valid event source. Since all access to theevent source and subscription information is guarded by a singlecritical section, no eventing function is ever able to access thisinformation without first obtaining the global lock and finding theevent source identified by this identifier in the list of event sources.This has little to no effect of performance, but guarantees concurrencyof threads.

An event source identifier is a concatenation of the UDN of the deviceand the service identifier. So, for example, if we have a UDN of“uuid:{3cbaf80e-401a-4c29-be7c-8573claf87f9}” and a service identifierof “clock:1”, then the event source identifier would be “uuid:{3cbaf80e-401a-4c29-be7c-8573claf87f9}clock:1”. This uniquely identifiesthe event source in the global list of event sources.

Event Source Registration

When a UPnP hosted service is registered via the Registrar, the DeviceHost will need to register this service as an event source. Part of theregistration process involves passing the list of evented statevariables and their initial values to the registration so it can be usedfor the initial event notification message for a new subscriber. Thislocal cache of state variables and their values will be updated eachtime an event notification is generated.

Event source registration is accomplished with theHrRegisterEventSource( ) API defined in FIG. 20. The following happenswhen HrRegisterEventSource( ) is called:

-   -   Lock global list of event sources    -   Find szEsid in list    -   If found        -   Return error    -   Else,        -   Create new UPNP_EVENT_SOURCE, copying the params to the            members of the struct        -   Set rgSubs member to NULL        -   Add item to list    -   Unlock list        Event Source Deregistration

When a hosted service is unpublished, and thereby no longer accessibleto control points, its associated event source is deregistered. This isaccomplished through the DeregisterEventSource( ) API defined in FIG.20. This API simply finds the event source in question, and removes itfrom the list of event sources. It then frees any data that this eventsource referenced. The following happens when HrDeregisterEventSource( )is called:

-   -   Lock global list of event sources    -   Find szEsid in list    -   If not found        -   Return error    -   Else,        -   Remove item from list    -   Unlock list    -   For each subscriber in the event source's subscriber list        -   Free the subscriber            Handling Subscribers

The Device Host is responsible for handling and maintaining thesubscriber list for each service that it hosts. The Device Host listensfor new SUBSCRIBE and UNSUBSCRIBE requests, parses them, and processesthem.

According to the UPnP architecture, UPnP devices terminates anysubscription that has not been renewed within the specified time period.To this end, the Device Host tracks each subscription and its specifiedlifetime, and terminates the subscription if it has not been renewed.

Incoming SUBSCRIBE and UNSUBSCRIBE requests are processed by the WebServer 154. The messages are parsed and validated for correctness beforebeing passed to the appropriate eventing manager object 153 forprocessing. The event subscription URL published in the descriptiondocument for a device contains a parameter to the Web Server that willindicate which device and service the request was sent to. If noservices match the identifier in the URL, “404 Not Found” is sent as aresponse.

Adding Subscribers

Handling SUBSCRIBE

When a SUBSCRIBE request is received, it is parsed to obtain therelevant pieces of information, namely, the Callback, NT, and Timeoutheaders. The Callback header contains the URL to which NOTIFY requestsshould be sent when an event is submitted. The NT header should contain“upnp:event” and nothing else. If a request contains something otherthan “upnp:event” in the NT header, it is ignored and “412 PreconditionFailed” is the response.

The Timeout header contains the subscriber's request for how long thesubscription should last. Per UPnP (see Appendix, “Universal Plug andPlay Device Architecture”), the device controls what the timeout reallyis, but it can choose to honor the subscriber's request. In the DeviceHost 100, the preferred timeout is specified when the service isregistered with the Host. If the timeout is 0, then subscriber's requestis always honored. If it is non-zero, then the subscriber's request isnever honored, rather the timeout specified to the Host API is usedinstead.

After the SUBSCRIBE request is parsed and validated, a new subscriptionID is generated, using the UuidCreate( ) function. This, along with thetimeout value calculated according to the algorithm discussed above, isplaced into an HTTP response message. After the response is sent, theSID and timeout values are associated with the subscriber.

Once a SUBSCRIBE is received and processed, a timer is started. Thetimer will expire after the timeout period for this subscriber haselapsed. If the timer expires, the subscription is terminated silently.This entails removing the subscriber from the list and intentionally notre-starting the timer.

If a SUBSCRIBE request contains a SID header, then it is considered are-SUBSCRIBE request. The SID header should match the one given to thesubscriber as a result of the response sent to its initial SUBSCRIBErequest. If the SID does not match, then the “404 Not Found” response issent.

If a SID header is included in the request, along with either an NTheader or Callback header, then the response “400 Bad Request” is sent.

If neither SID, NT, nor Callback headers are present, the response “412Precondition failed” is sent.

When the SID matches an existing subscription's SID maintained by theDevice Host, the subscription's timer is reset to the original timeoutvalue. The response “200 OK” is then sent, along with the same SIDheader as was included in the request along with the same timeout valueincluded in the original subscription response.

HrAddSubscriber( )

The HrAddSubscriber( ) API defined in FIG. 20 operates as follows:

-   -   Create new UPNP_SUBSCRIBER, filling in information from the        request    -   Generate new SID by calling UuidCreate( )    -   Initialize renewal counter to 0    -   Initialize event queue to empty    -   Create new unnamed event for event queue    -   Call RegisterWaitForSingleObject( ) passing in the        UPNP_WAIT_PARAMS struct    -   Lock event source list    -   Look up the szEsid in the event source list        -   If not found, it means the subscriber attempted to subscribe            to an event source that is no longer available. Return 404            Not Found.    -   The timeout value is the one passed to HrAddSubscriber( )    -   Create a new timer queue timer for the subscriber, using the        timeout value. The parameter to the timer will be the        UPNP_EVENT_SOURCE and the SID for the subscriber contained in        the UPNP_RENEWAL structure. It can't be the UPNP_SUBSCRIBER        itself, because it may get deleted prior to executing the        callback function.    -   Set the in/out parameter pcsecTimeout to this timeout that was        chosen.    -   Add Subscriber to list of subscribers for that event source    -   Unlock event source list    -   Call the HrSubmitEventZero( ) API below for this event source        (defined below)        Renewing Subscribers

The HrRenewSubscriber( ) API operates as follows:

-   -   Lock global event source list    -   Lookup the event source passed in        -   If event source is not found, unlock list then respond with            404 Not Found    -   If SID matches one in the list of subscribers for this event        source        -   Delete (non-blocking) previous timer for subscriber        -   Increment renewal counter        -   Determine the timeout for the renewal in the same manner as            for HrAddSubscriber( )        -   Create new timer for subscriber with the same timeout,            passing the UPNP_RENEWAL structure as the pvParam    -   Unlock event source list    -   If renewal was successful        -   Compose response, including same SID and Timeout            Renewal Timer Callback

The Device Host handles renewal timer callback as follows:

-   -   -   -   -   The pvParam points to the UPNP_RENEWAL structure for                    this subscription                -   Lock the event source list

    -   Iterate through each event source, looking for one that matches        the szEsid member of the structure

    -   If found,        -   Iterate through the list of subscribers for that event            source looking for one with a SID that matches szSid.        -   If found,            -   Compare the cRenewals member of that UPNP_SUBSCRIBER                structure with the iRenewal member of the UPNP_RENEWAL            -   If they are the same,                -   Remove the subscriber from the list                -   Unlock the list                -   Queue a work item to do the following:                -    Issue a blocking UnregisterWait( ) on the                    subscriber's wait handle                -    Issue a blocking DeleteTimerQueueTimer( ) on the                    subscriber's timer handle                -    Free the memory used by the structure                -    Free the structure

    -   If not found        -   Unlock the list            How a SUBSCRIBE is processed

The Device Host processes subscribe requests as follows:

-   -   Receive request from network code    -   Parse request into headers    -   If method is SUBSCRIBE        -   Validate headers        -   If validation succeeded            -   If this is a re-SUBSCRIBE            -   Call HrRenewSubscriber( )            -   Else if it is a normal SUBSCRIBE            -   Call HrAddSubscriber( )        -   Else            -   Respond with “400 Bad Request”                Removing Subscribers

The Device Host removes a subscriber from an event source as follows:

-   -   Lock the global event source list    -   Remove the subscriber from the event source    -   Unlock the list    -   Queue a work item to do the following:        -   Issue a blocking UnregisterWait( ) on the subscriber's wait            handle        -   Issue a blocking DeleteTimerQueueTimer( ) on the            subscriber's timer handle        -   Free the memory used by the structure        -   Free the structure            Handling UNSUBSCRIBE

When an UNSUBSCRIBE request is received by the Web Server 154, it isparsed to obtain the relevant pieces of information, namely, the querystring and the SID header. The query string contains the identifier ofdevice and the service from which the subscription should be removed.

If the NT or Callback header is present, the response “400 Bad Request”is sent.

If the SID header does not match an existing subscription for therequested service, the response “404 Not Found” is sent.

If the SID header is absent or is empty, then the response “412Precondition Failed” is sent.

After the UNSUBSCRIBE request is parsed and validated, the subscriptionto which the SID belongs is accessed. Its timer is stopped and thesubscription is removed from the list. Then, the response “200 OK” issent.

HrRemoveSubscriber( )

The HrRemoveSubscriber( ) API operates as follows:

-   -   Lock global event source list    -   Find the event source referenced in the message        -   If event source is not found, unlock list then respond with            404 Not Found    -   If SID matches one in the list of subscribers for this event        source        -   Remove subscriber from list    -   Unlock event source list    -   Queue a work item to do the following:        -   Issue a blocking UnregisterWait( ) on the subscriber's wait            handle        -   Issue a blocking DeleteTimerQueueTimer( ) on the            subscriber's timer handle        -   Free the memory used by the structure        -   Free the structure            How an UNSUBSCRIBE is processed

The Device Host process the unsubscribe request as follows:

-   -   Receive request from network code    -   Parse request into headers    -   If method is UNSUBSCRIBE        -   Validate headers        -   If validation succeeded            -   Send “200 OK” response            -   Call HrRemoveSubscriber( )        -   Else            -   Respond with “400 Bad Request”                Submitting Event Notifications

When one or more evented service state variables change, the serviceMUST submit their changes as an event notification. The Device Hosthandles the submission of the NOTIFY request automatically. The hostedservice communicates the fact that one or more state variables havechanged by calling the IUPnPEventSink::OnStateChanged( ) method. Thiswill inform the Device Host that it needs to query the hosted servicefor the values of these variables.

The HrSubmitEvent( ) API defined in FIG. 20 utilizes a UPnP_Event datastructure defined in FIG. 19.

Event Submission Architecture

The HrSubmitEvent( ) API relies on an “event queue” 602-603 persubscriber (as shown in the event submission architecture 600 of FIG.21) in which to place pending event notifications. When an event issubmitted, it is placed on the queue for each subscriber for a pool ofworker threads 610 to act on sequentially. Each event queue issequential. An item closer to the front of the queue is always processedprior to an item toward the back of the queue. Event zero notificationsfor a subscriber always is first in the queue, before any other eventnotifications to that subscriber.

When an item is added to the queue, an event is signaled so that aworker thread can begin processing it. Once an item is removed from thequeue for processing, the worker thread will handle sending the eventnotification to each subscriber. The heuristics defined here ensure thateach subscriber's event queue is processed sequentially, with the nextitem in the queue not processed until the previous item is complete.

In more detail, when the OnStateChanged( ) method is called by aservice, the following happens:

-   -   The eventing manager object calls a function to query the value        of each DISPID that has changed.    -   The object then calls the HrSubmitEvent( ) API passing the event        source identifier (which is composed of the concatenation of the        UDN and service identifier) and the name of each variable and        its new value. It obtains the names of each variable from a        table that maps DISPIDs to state variable names.

The HrSubmitEvent( ) API then does the following:

-   -   It first attempts to find the event source identified by the        caller in the global list of event sources registered.    -   Locks the global event source list    -   Enumerates each item looking for the event source identifier it        was passed    -   If the event source was not found in the list, the API unlocks        the list and returns a failure code to the caller immediately.    -   The XML body of the event notification comes from the        szEventBody parameter.    -   Then, for each subscriber in the list of subscribers for this        event source:        -   If the sequence number>0            -   Create a UPNP_EVENT structure.            -   Copy szEventBody into it            -   Insert the UPNP_EVENT item at the tail of the list of                pending send items            -   If the send queue was empty prior to adding this item,                -   Signal the send queue event for this subscriber's                    queue    -   Unlock the event source list

The Send Queue Worker Thread operates as follows:

-   Meanwhile, a pool of worker threads is waiting on each subscriber's    queue event-   When a queue event is signaled, the worker wakes up and does the    following:    -   The pvParam will be cast to a UPNP_WAIT_PARAMS struct which        indicates which event source and subscriber the worker is        dealing with    -   Lock the global event source list    -   Iterate the global event source list looking for the szEsid        member of the UPNP_WAIT_PARAMS struct.    -   If found,        -   Iterate its list of subscribers looking for the szSid member            of the UPNP_WAIT_PARAMS struct            -   If found,                -   Assert that the list of event for this subscriber is                    not empty. If the worker thread woke up, then it                    must have been because an item was added to the                    queue.                -   Remove the first UPNP_EVENT structure from the list                    of events for this subscriber                -   local variable fempty=IsListEmpty( )                -   Copy the callback URL and SID from the subscriber to                    local variables                -   Copy the current sequence number to a local variable                    and then increment it                -   Unlock the global event source list                -   Compose the headers for the event message using the                    local sequence number and SID.                -   Use the body from the UPNP_EVENT struct

The message should be of the following form: NOTIFY uri HTTP/1.1 HOST:host:port CONTENT-TYPE: text/xml CONTENT-LENGTH: bytes in body NT:upnp:event NTS: upnp:propchange SID: SID SEQ: sequenceNo <e:propertysetxmlns:e=“urn:schemas-upnp-org:event-1-0”>  <e:property>  <variableName1>newValue1<variableName1>  </e:property>  <e:property>  <variableName2>newValue2<variableName2>  </e:property></e:propertyset>

-   -   -   -   -   uri is the Request-URI portion of the EventSinkURL                    passed in the “Callback” header of a SUBSCRIBE                    request. This comes from the szUrl member of                    UPNP_SUBSCRIBER.                -   host is the hostname portion of the EventSinkURL                    passed in the “Callback” header of a SUBSCRIBE                    request. This also comes from the szUrl member of                    UPNP_SUBSCRIBER.                -   port is the port portion of the EventSinkURL passed                    in the “Callback” header of a SUBSCRIBE request.                    This also comes from the szUrl member of                    UPNP_SUBSCRIBER.                -   SID is the subscription identifier generated for the                    response to a SUBSCRIBE request. This comes from the                    szSid member of UPNP_WAIT_PARAMS.                -   sequenceNo is the sequence number generated as part                    of event submission described earlier in this                    section. This is kept locally as described above.                -   WinINET is then used to open a connection to the                    subscriber and send the HTTP request. Since there is                    no recourse for the Device Host at this point, any                    error code returned from the send operation is                    ignored except for diagnostic purposes.                -   Send the message to the local callback URL                -   Free the body in the UPNP_EVENT struct                -   Free the UPNP_EVENT struct                -   If fEmpty is FALSE                -    Signal the event again so another worker thread can                    pick this item up

The response to a NOTIFY can be any of the following:

-   -   “412 Precondition Failed”—An invalid or missing SID was        encountered on a NOTIFY request, with an NT header of        “upnp:event”    -   “400 Bad Request”—The NT or NTS header was not present    -   “200 OK”—NOTIFY was accepted and processed.

The response to a NOTIFY request is ignored since there is no recoursefor the device to have in the case of failure. Therefore, these returncodes will be used strictly for diagnostic purposes.

Sending the Initial Event Notification

The initial event notification is sent using the HrSubmitEventZero( )API defined in FIG. 20. The following is the implementation of this API:

-   -   Lock the event source list    -   Ensure that the event source matches on in the list of event        sources. If not, return.    -   Ensure that the SID passed in matches one of the subscribers in        the list. If not, return.    -   Find the SID of the subscriber in the list of subscribers for        this event source    -   Copy the body passed in szEventBody to a new UPNP_EVENT        structure    -   Add the UPNP_EVENT structure to the list of events for this        subscriber    -   Assert that the event list for this subscriber was empty prior        to adding this item to the queue    -   Signal the queue event for this subscriber    -   Unlock the event source list        Web Server Interface to the Eventing Manager Object

All requests from a control point (e.g., at the UPnP Devices 120-122 ofFIG. 1) that are sent to a Device Host computer pass through the WebServer 154 that determines if the request is related to a device hostedon the machine. If so, they are processed further. When the Device Hostpublishes a device and its services, each service's event subscriptionURL will point at the Web Server. The query string part of the URLidentifies the device and service for which a request is destined. Therequest method determines if it is related to control, eventing, orpresentation. An example event subscription URL is as follows:

-   -   http://danielwe/upnp/web-server-api.dll?uuid:{53030327-9171-48e8-9589-b89456ea9054}+clock.1

In the case of eventing, the request method will be either SUBSCRIBE orUNSUBSCRIBE. Once the Web Server has determined this, it processes therequest as follows:

-   -   If the method is SUBSCRIBE, determine if this is a SUBSCRIBE or        re-SUBSCRIBE request:        -   Query the NT header. If it exists, and is not “upnp:event”,            respond with “412 Precondition Failed.” If the NT header            exists and is valid, the request is now parsed as a            SUBSCRIBE request. If the NT header did not exist, the            request is considered a re-SUBSCRIBE request.        -   If the request is a SUBSCRIBE request            -   Query the Callback header. If it exists, verify that it                is a valid HTTP URL and keep it in a local variable. If                it is invalid or not present, send a “412 Precondition                Failed” response.            -   Query the Timeout header. If it exists, convert it to a                base 10 integer, and keep it in a local variable. If not                use a default timeout of 21,600 seconds (6 hours).            -   Query for the SID header and ensure that it is not                present. If it is, send a “400 Bad Request” response.            -   Using the query string passed to the Web Server, ask the                registrar to return the Eventing Manager object                associated with that query string.            -   Call the IUPnPEventingManager::AddSubscriber( ) method,                passing in the callback URL and timeout queried from the                headers. The method will return the SID that can be used                in the response.            -   If the method call returns an error, map the error to an                appropriate response code and send the response.        -   Else, if the request is a re-SUBSCRIBE request            -   Query the SID header. If it exists, ensure that the NT                and Callback headers do not. If the latter is true, send                a “400 Bad Request” response. If the SID header was not                present, or was empty, respond with “412 Precondition                Failed.”            -   Query the Timeout header. If it exists, convert it to a                base 10 integer, and keep it in a local variable. If not                use a default timeout of 21,600 seconds (6 hours).            -   Using the query string passed to the Web Server, ask the                registrar to return the Eventing Manager object                associated with that query string.            -   Call the IUPnPEventingManager::RenewSubscriber( )                method, passing in the SID and timeout queried from the                headers.            -   If the method call returns an error, map the error to an                appropriate response code and send the response (i.e.                SID invalid).        -   If the addition or renewal of a subscriber succeeded,            compose the response by setting the following headers:            -   the DATE header to the current date            -   the SERVER header to the version of the operating system            -   For a SUBSCRIBE, the SID header will be the SID returned                from IUPnPEventingManager::AddSubscriber( )            -   For a re-SUBSCRIBE, the SID header will be the same SID                header queried from the request            -   The TIMEOUT header will be the csecTimeout result from                the AddSubscriber or RenewSubscriber( ) methods.    -   If the method is UNSUBSCRIBE        -   Query the request for the SID header. If not present respond            with “412 Precondition Failed.”        -   Query for NT and Callback headers. If either are present,            respond with “400 Bad Request.”        -   Using the query string passed to the Web Server, ask the            registrar to return the Eventing Manager object associated            with that query string.        -   Call the IUPnPEventingManager::RemoveSubscriber( ) method,            passing in the SID queried from the headers.        -   If the method call returns an error, map the error to an            appropriate response code and send the response (i.e. SID            invalid).

The response to an UNSUBSCRIBE does not have any additional headers sono additional work is required to send it.

Exemplary Computer Hardware

FIG. 22 and the following discussion are intended to provide a brief,general description of a suitable computer which may be used to run SSDPservices and SSDP clients described above. This conventional computer820 (such as personal computers, laptops, palmtops or handheld-PCs,set-tops, servers, mainframes, and other variety computers) includes aprocessing unit 821, a system memory 822, and a system bus 823 thatcouples various system components including the system memory to theprocessing unit 821. The processing unit may be any of variouscommercially available processors, including Intel x86, Pentium andcompatible microprocessors from Intel and others, including Cyrix, AMDand Nexgen; Alpha from Digital; MIPS from MIPS Technology, NEC, IDT,Siemens, and others; and the PowerPC from IBM and Motorola. Dualmicroprocessors and other multi-processor architectures also can be usedas the processing unit 821.

The system bus may be any of several types of bus structure including amemory bus or memory controller, a peripheral bus, and a local bus usingany of a variety of conventional bus architectures such as PCI, VESA,AGP, Microchannel, ISA and EISA, to name a few. The system memoryincludes read only memory (ROM) 824 and random access memory (RAM) 825.A basic input/output system (BIOS), containing the basic routines thathelp to transfer information between elements within the computer 820,such as during start-up, is stored in ROM 824.

The computer 820 further includes a hard disk drive 827, a magnetic diskdrive 828, e.g., to read from or write to a removable disk 829, and anoptical disk drive 830, e.g., for reading a CD-ROM disk 831 or to readfrom or write to other optical media. The hard disk drive 827, magneticdisk drive 828, and optical disk drive 830 are connected to the systembus 823 by a hard disk drive interface 832, a magnetic disk driveinterface 833, and an optical drive interface 834, respectively. Thedrives and their associated computer-readable media provide nonvolatilestorage of data, data structures, computer-executable instructions, etc.for the computer 820. Although the description of computer-readablemedia above refers to a hard disk, a removable magnetic disk and a CD,it should be appreciated by those skilled in the art that other types ofmedia which are readable by a computer, such as magnetic cassettes,flash memory cards, digital video disks, Bernoulli cartridges, and thelike, may also be used in the exemplary operating environment.

A number of program modules may be stored in the drives and RAM 825,including an operating system 835, one or more application programs 836,other program modules 837, and program data 838, as well as the DeviceHost 100 and API 102 (FIG. 1).

A user may enter commands and information into the computer 820 througha keyboard 840 and pointing device, such as a mouse 842. Other inputdevices (not shown) may include a microphone, joystick, game pad,satellite dish, scanner, or the like. These and other input devices areoften connected to the processing unit 821 through a serial portinterface 846 that is coupled to the system bus, but may be connected byother interfaces, such as a parallel port, game port or a universalserial bus (USB). A monitor 847 or other type of display device is alsoconnected to the system bus 823 via an interface, such as a videoadapter 848. In addition to the monitor, computers typically includeother peripheral output devices (not shown), such as speakers andprinters.

The computer 820 operates in a networked environment using logicalconnections to one or more remote computers, such as a remote computer849. The remote computer 849 may be a server, a router, a peer device orother common network node, and typically includes many or all of theelements described relative to the computer 820, although only a memorystorage device 850 has been illustrated in FIG. 22. The logicalconnections depicted in FIG. 22 include a local area network (LAN) 851and a wide area network (WAN) 852. Such networking environments arecommonplace in offices, enterprise-wide computer networks, intranets andthe Internet.

When used in a LAN networking environment, the computer 820 is connectedto the local network 851 through a network interface or adapter 853.When used in a WAN networking environment, the computer 820 typicallyincludes a modem 854 or other means for establishing communications(e.g., via the LAN 851 and a gateway or proxy server 855) over the widearea network 852, such as the Internet. The modem 854, which may beinternal or external, is connected to the system bus 823 via the serialport interface 846. In a networked environment, program modules depictedrelative to the computer 820, or portions thereof, may be stored in theremote memory storage device. It will be appreciated that the networkconnections shown are exemplary and other means of establishing acommunications link between the computers may be used.

In accordance with the practices of persons skilled in the art ofcomputer programming, the present invention is described above withreference to acts and symbolic representations of operations that areperformed by the computer 820, unless indicated otherwise. Such acts andoperations are sometimes referred to as being computer-executed. It willbe appreciated that the acts and symbolically represented operationsinclude the manipulation by the processing unit 821 of electricalsignals representing data bits which causes a resulting transformationor reduction of the electrical signal representation, and themaintenance of data bits at memory locations in the memory system(including the system memory 822, hard drive 827, floppy disks 829, andCD-ROM 831) to thereby reconfigure or otherwise alter the computersystem's operation, as well as other processing of signals. The memorylocations where data bits are maintained are physical locations thathave particular electrical, magnetic, or optical propertiescorresponding to the data bits.

Exemplary Embedded Computing Device

FIG. 23 is intended to provide a brief, general description of asuitable embedded computing device 900 which may be used in theillustrated implementation of the invention. The embedded computingdevice 900 can be any variety of device incorporating electronics tocontrol operational functions (operational circuitry 906), and in whichcomputing and networking capabilities are embedded. For example, devicesin which computing and networking functions can be embedded includecommunications devices (e.g., telephones, cell phones, audio and videoconferencing systems, 2-way radios, etc.), office equipment (printers,fax machines, copiers, dictation, etc.), audio-video equipment (audioand video recorders and players, including televisions, radio receivers,compact disk (CD), digital video disk (DVD), camcorders, etc.),entertainment devices (set-top boxes, game consoles, etc.), environmentcontrol equipment (thermostats, heating/ventilation/air-conditioningequipment, light switches, etc.), security systems, home appliances(coffee makers, dishwashers, clothes washer/dryer), automobiles, publicfacilities equipment (signs, traffic signals, etc.), manufacturingequipment, and many others.

The device 900 includes a processing unit 902, and a memory 904 toprovide embedded computing capability. The processing unit 902 hashardware interfaces to the operational circuitry 906 that operatesdevices functions. The processing unit 902 can be a microprocessor ormicro-controller, such as are available from Intel, Motorola, IBM, andothers. The memory 904 preferably incorporates RAM and ROM to holdsoftware and data for basic operating code as well as for userapplications, including the Device Host 100 and API 102 (FIG. 1).

The device 900 also includes a network adapter 908 for connecting with anetwork media 910 that is interconnected with the computer network inwhich the authoritative names registry (described below) is implementedin accordance with the invention. The network adapter 908 can be anetwork interface card (or chip set integrated on a single board withthe processing unit 902) appropriate to the particular network media910. The network media can be any of various wired or wireless networkmedia, including Ethernet, IEEE 1394 (a.k.a. firewire), radio frequency(including satellite, cell, pager, commercial signal sideband, etc.),power line carrier (PLC), phone line, and television cable, amongothers.

Illustrative Pervasive Computing Environment

FIG. 24 illustrates a pervasive computing environment 1000, such as maybe installed in a home, office or public place, which includes a largenumber of embedded computing devices, such as the illustrated device 900(FIG. 23). The pervasive computing environment 1000 includes personalcomputers 1002, 1004 (e.g., of the type shown in FIG. 22) connected viaa local area network (LAN) 1006. The PC 1002 is connected via auniversal serial bus 1016 to a telephone modem 1010, XDSL interface 1011or a cable modem 1012, which in turn provide a connection with thecomputer network, e.g., the Internet.

Various embedded computing devices also connect to the computer networkvia various network connections to the PCs 1002, 1004. These include anaudio device 1014 (e.g., speakers, radio tuner, microphone), and printer1015 which connect to the PC 1004 through a USB 1017. Also, a digitalcamera 1020, a handheld PC(H/PC) 1021 and another personal computingdevice 1022 connect via an infrared port (IRDA) 1024, which alsoattaches to the PC 1004 through the USB 1017. Also, lighting switches1030 and like home appliances are connected via an A/C power line-basednetworking 1032 to the PC 1002. Further, a chain of IEEE 1394 cables1048 connect a digital TV 1040, DVD player 1041, digital video camcorder(DV/DVC) 1042, an audio device 1043 (e.g., CD player/recorder, radioreceiver, amplifier, and like audio system component), and a gameconsole 1044. Devices, such as a portable telephone 1050 and remotecontrol 1051, have a radio frequency network connection with the PC1004.

With their various inter-networked connections, the embedded computingdevices are “visible” and accessible from a client device also connectedto the computer network.

Appendix Device Host API Reference IUPNPDEVICECONTROL

The IUPnPDeviceControl interface serves as the central point ofmanagement for the device and its service objects

IDL Reference: [  uuid(f5bcf2f0-f411-4da5-805c-1ea0afdb0869), pointer_default(unique), ] interface IUPnPDeviceControl : IUnknown {  [helpstring(“method Initialize”)]   HRESULT Initialize(   [in] BSTR bstrXMLDesc,   [in] BSTR  bstrInitString,    [in] BSTR bstrDeviceIdentifier);   [helpstring(“method GetServiceObject”)]  HRESULT GetServiceObject(   [in]  BSTR  bstrUDN,   [in]  BSTR bstrServiceId,   [out, retval] IDispatch ** ppdispService); }

When to Implement

Implemented in the device control object by the hosted device developer.

When to Use

The device host uses this interface to initialize the device and getaccess to the service objects for related control requests.

Methods and Properties Method Description Initialize Initializes thedevice control object with the device description and a device specificinitialization string GetServiceObject Returns an IDispatch pointer tothe service object requested by the device hostIUPnPDeviceControl::Initialize

The IUPnPDeviceControl::Initialize method is invoked by the device hostto initialize the device. HRESULT Initialize (   BSTR bstrXMLDesc,  BSTR bstrInitString,   BSTR bstrDeviceIdentifier );

Parameters:

bstrXMLDesc

-   -   [in] Specifies the full XML device description as published by        the device host.

bstrInitString

-   -   [in] Specifies a device specific initialization string

bstrDeviceIdentifier

-   -   [in] Device identifier obtained as a result of a call to        IUPnPRegistrar::RegisterDevice( ) and        IUPnPRegistrar::RegisterRunningDevice( ).

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns on of the COM error codes defined in WinError.h.

IUPnPDeviceControl::GetServiceObject

The IUPnPDeviceControl::GetServiceObject method is used to retrieve anIDispatch pointer to the service object referenced by the device hostHRESULT GetServiceObject(  BSTR bstrUDN,  BSTR bstrServiceId,  IDispatch**pdispService );

Parameters:

bstrUDN

-   -   [in] Specifies the UDN of the device

bstrServiceId

-   -   [in] Specifies the Service ID of the service

pdispService

-   -   [out, retval] Contains the address of an IDispatch pointer to        the service object

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

Remarks:

This method is called by the device host when a control request isreceived for a particular service. If the service object already exists,then it returns a pointer to the existing instance, otherwise itinstantiates a new service object.

IUPNPREGISTRAR

The IUPnPRegistrar object allows the registration of the devices/bridgesthat will run in the context of the device host.

IDL Reference: [  uuid(204810b6-73b2-11d4-bf42-00b0d0118b56), pointer_default(unique) ] interface IUPnPRegistrar : IUnknown { HRESULT RegisterDevice(   [in] BSTR bstrXMLDesc,   [in] BSTRbstrProgIDDeviceControlClass,   [in] BSTR bstrInitString,   [in] BSTRbstrContainerId,   [in] BSTR bstrResourcePath,   [in] long  nLifeTime,   [out, retval] BSTR  * pbstrDeviceIdentifier);  HRESULTRegisterRunningDevice(   [in] BSTR bstrXMLDesc,   [in] IUnknown *punkDeviceControl,   [in] BSTR bstrInitString,   [in] BSTRbstrResourcePath,   [in] long  nLifeTime    [out, retval] BSTR *pbstrDeviceIdentifier);  HRESULT RegisterDeviceProvider(   [in] BSTRbstrProviderName,   [in] BSTR bstrProgIDProviderClass,   [in] BSTRbstrInitString,   [in] BSTR bstrContainerId);  HRESULTGetUniqueDeviceName(   [in] BSTR bstrDeviceIdentifier,    [in] BSTR  bstrTemplateUDN,   [out, retval] BSTR  * pbstrUDN);  HRESULTUnregisterDevice(   [in] BSTR bstrDeviceIdentifier,    [in] BOOLfPermanent);  HRESULT UnegisterDeviceProvider(   [in] BSTRbstrProviderName); }

When to Implement

UPnP Device Host implements this interface.

When to Use

You should use this interface to register a device for use on a UPnPnetwork.

Methods and Properties Method Description RegisterDevice Staticallyregisters a device with the device host RegisterRunningDevice Registersa device that is already running with the device h

RegisterDeviceProvider Registers a device provider with the device hostGetUniqueDeviceName Returns the UDN of the device UnregisterDeviceUnregisters and unloads the device from the device hostUnregisterDeviceProvider Unregisters and unloads a device provider fromthe deviceIUPnPRegistrar::RegisterDevice

The IUPnPRegistrar::RegisterDevice method registers a device with thedevice host framework, persists this information, and returns a deviceidentifier, which would be used while unregistering or re-registeringthe device. The device is subsequently published on the network. HRESULTRegisterDevice(   BSTR bstrXMLDesc,   BSTR bstrProgIDDeviceControlClass,  BSTR bstrInitString,   BSTR bstrContainerId,   BSTR bstrResourcePath,  LONG   nLifeTime,   BSTR *pbstrDeviceIdentifier );

Parameters:

bstrXMLDescr

-   -   [in] The XML device description template, as described in        section 3.1.

bstrProgIDDeviceControlClass

-   -   [in] The ProgID of a device object that implements        IUPnPDeviceControl.

This must be an in-process COM server (CLSTX_INPROC_SERVER)

bstrInitString

-   -   [in] The device specific initialization string that gets passed        on to IUPnPDeviceControl::Initialize.

bstrContainerId

-   -   [in] A string that identifies the process group in which the        device belongs. All devices with the same container identifier        will be contained in the same process.

bstrResourcePath

-   -   [in] Location of the resource directory of the device. This        resource directory will contain the various icon files and        service descriptions specified in the device description        template.

nLifeTime

-   -   [in] SSDP timeout (in seconds) of the device after which the        announcements will be refreshed. If the value is 0, then a        default timeout of 1800 seconds is used. If a timeout of less        900 seconds is specified, then an E_INVALIDARG is returned.

pbstrDeviceIdentifier

-   -   [out, retval] Device identifier that will be used when        unregistering or re-registering the device

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPnPRegistrar::RegisterRunningDevice

The IUPnPRegistrar::RegisterRunningDevice method registers a runningdevice with the device host framework and returns a device identifier tobe used when unregistering or reregistering the device. The device issubsequently published on the network. HRESULT RegisterRunningDevice(  BSTR bstrXMLDesc,   IUnknown *punkDeviceControl,   BSTRbstrInitString,   BSTR bstrResourcePath,   LONG nLifeTime,   BSTR*pbstrDeviceIdentifier );

Parameters:

bstrXMLDescr

-   -   [in] The XML device description template, as described in        section 3.1.

punkDeviceControl

-   -   [in] IUnknown pointer to the device's device control class

bstrInitString

-   -   [in] The device specific initialization string that gets passed        to IUPnPDeviceControl::Initialize.

bstrResourcePath

-   -   [in] Location of the resource directory of the device. This        resource directory will contain the various icon files and        service descriptions specified in the device description        template.

nLifeTime

-   -   [in] SSDP timeout (in seconds) of the device after which the        announcements will be refreshed.

pbstrDeviceIdentifier

-   -   [out, retval] Device identifier that will be used when        unregistering or re-registering the device

Return Values:

-   -   If the method succeeds, the return value is S_OK. Otherwise, the        method returns one of the COM error codes defined in WinError.h.        IUPnPRegistrar::RegisterDeviceProvider

The IUPnPRegistrar::RegisterDeviceProvider method registers a deviceprovider with the device host framework. The device provider, however,is not published on the network. Instead, it should create devicesdynamically and register them on the fly withIUPnPRegistrar::RegisterRunningDevice. HRESULT RegisterDeviceProvider( BSTR bstrProviderName,  BSTR bstrProgIDProviderClass,  BSTRbstrInitString,  BSTR bstrContainerId );

Parameters:

bstrProviderName

-   -   [in] Name of the device provider

bstrProgIDProviderClass

-   -   [in] The ProgID of the IUPnPDeviceProvider interface that has        already been registered with the device host framework

bstrInitString

-   -   [in] A device provider specific initialization string.

bstrContainerId

-   -   [in] A string that identifies the process group in which the        device provider belongs. All devices/device providers with the        same container identifier will be contained in the same process.

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPnPRegistrar::GetUniqueDeviceName

The IUPnPRegistrar::GetUniqueDeviceName method retrieves the UDN thatthe device host has generated for the device. The UDNs specified fordevices in the device description template get replaced with globallyunique UDNs during registration. HRESULT GetUniqueDeviceName(   BSTRbstrDeviceIdentifier,   BSTR bstrTemplateUDN,   BSTR *pbstrUDN );

Parameters:

bstrDeviceIdentifier

-   -   [in] The identifier returned from

IUPnPRegistrar::IUPnPRegisterDevice( ) or

IUPnPRegistrar::RegisterRunningDevice( ).

bstrTemplateUDN

-   -   [in] UDN specified in the device description template

pbstrUDN

-   -   [out, retval] The device UDN generated by the device host

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPnPRegistrar::UnregisterDevice

The IUPnPRegistrar::UnregisterDevice method unregisters the device fromthe device host framework. It allows a device to be temporarily orpermanently unregistered. HRESULT UnregisterDevice(   BSTRbstrDeviceIdentifier,   BOOL fPermanent );

Parameters:

bstrDeviceIdentifier

-   -   [in] The device identifier returned from

IUPnPRegistrar::RegisterDevice( ) and

IUPnPRegistrar::RegisterRunningDevice( ).

fPermanent

-   -   [in] A flag to determine if the device should be deleted        permanently (TRUE) or not (FALSE).

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

Remarks:

This method will remove a device from the device host. If the flag isset, then it will permanently delete the device, otherwise, it willpersist the mapping of the device identifier (returned fromIUPnPRegistrar::RegisterDevice or IUPnPRegistrar::RegisterRunningDevice)with the UDN of the device generated by the device host. Consequently,on re-registration, the previous UDN associated with the device will beretained.

IUPnPRegistrar::UnregisterDeviceProvider

The IUPnPEventSource::UnregisterDeviceProvider method permanentlyunregisters and unloads the device provider from the device host.HRESULT UnregisterDeviceProvider(   BSTR bstrProviderName );

Parameters:

bstrProviderName

-   -   [in] Provider Name, as specified in the        IUPnPRegistrar::RegisterDeviceProvider.

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPNPREREGISTRAR

The IUPnPReregistrar object allows the device host to re-register UPnPdevice(s) with the device host.

IDL Reference [  uuid(d9b9bf6a-3986-4071-929e-4ff70e44a5b0), pointer_default(unique), ] interface IUPnPReregistrar : IUnknown { [helpstring(“method ReregisterDevice”)]   HRESULT ReregisterDevice(   [in] BSTR  bstrDeviceIdentifier,    [in] BSTR   bstrXMLDesc    [in]BSTR   bstrProgIDDeviceControlClass,    [in] BSTR   bstrInitString,   [in] BSTR   bstrContainerId,    [in] LONG   nLifeTime); [helpstring(“method ReregisterRunningDevice”)]  HRESULTReregisterRunningDevice(   [in] BSTR    bstrDeviceIdentifier,    [in]BSTR    bstrXMLDesc    [in] IUnknown  * punkDeviceControl,    [in] BSTR   bstrInitString,    [in] BSTR    bstrResourcePath,    [in] LONG   nLifeTime); }

When to Implement

UPnP Device Host implements this interface.

When to use

The caller should use this interface to re-register devices with the UDNoriginally generated by the device host on a call toIUPnPRegistrar::RegisterDevice( ) andIUPnPRegistrar::RegisterRunningDevice( ).

Methods and Properties Method Description ReregisterDevice Re-registersthe static device with the same original UDN ReregisterRunningDeviceRe-registers the running device with the same original UD

IUPnPReregistrar::ReregisterDevice

The IUPnPReregistrar::ReregisterDevice method re-registers a device withthe device host. HRESULT ReregisterDevice(   BSTR bstrDeviceIdentifier,  BSTR bstrXMLDesc,   BSTR bstrProgIDDeviceControlClass,   BSTRbstrInitString,   BSTR bstrContainerId,   BSTR bstrResourcePath,   LONG  nLifeTime );

Parameters:

bstrDeviceIdentifier

-   -   [in] The device identifier returned by        IUPnPRegistrar::RegisterDevice( ) and        IUPnPRegistrar::RegisterRunningDevice( ).

bstrXMLDescr

-   -   [in] The XML device description template, as described in        section 3.1.

bstrProgIDDeviceControlClass

-   -   [in] The ProgID of a device object that implements        IUPnPDeviceControl. This must be an in-process COM server        (CLSTX_INPROC_SERVER)

bstrInitString

-   -   [in] The device specific initialization string that gets passed        on to IUPnPDeviceControl::Initialize.

bstrContainerId

-   -   [in] A string that identifies the process group in which the        device belongs. All devices with the same container identifier        will be contained in the same process.

bstrResourcePath

-   -   [in] Location of the resource directory of the device. This        resource directory will contain the various icon files and        service descriptions specified in the device description        template.

nLifeTime

-   -   [in] SSDP timeout (in seconds) of the device after which the        announcements will be refreshed.

Return Values:

-   -   If the method succeeds, the return value is S_OK. Otherwise, the        method returns one of the COM error codes defined in WinError.h.        IUPnPReregistrar::ReregisterRunningDevice

The IUPnPReregistrar::ReregisterDevice method re-registers a runningdevice with the device host. HRESULT ReregisterRunningDevice(  BSTRbstrDeviceIdentifier,  BSTR bstrXMLDesc,  IUnknown *punkDeviceControl, BSTR bstrInitString,  BSTR bstrResourcePath,  LONG nLifeTime );

Parameters:

bstrDeviceIdentifier

-   -   [in] The device identifier returned by        IUPnPRegistrar::RegisterDevice( ) and        IUPnPRegistrar::RegisterRunningDevice( ).

bstrXMLDescr

-   -   [in] The XML device description template, as described in        section 3.1.

punkDeviceControl

-   -   [in] IUnknown pointer to the device's device control class

bstrInitString

-   -   [in] The device specific initialization string that gets passed        to IUPnPDeviceControl::Initialize.

bstrResourcePath

-   -   [in] Location of the resource directory of the device. This        resource directory will contain the various icon files and        service descriptions specified in the device description        template.

nLifeTime

-   -   [in] SSDP timeout (in seconds) of the device after which the        announcements will be refreshed.

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPNPDEVICEPROVIDER

The IUPnPDeviceProvider object allows a device provider to be startedand stopped.

IDL Reference [   object,   uuid(e5191547-d010-4431-8004-bffb4f8c5d9f),  pointer_default(unique),   version(1.0) ] interfaceIUPnPDeviceProvider : IUnknown {  [helpstring(“method Start”)]  HRESULTStart(   [in] BSTR bstrInitString);  [helpstring(“method Stop”)] HRESULT Stop( ); }

When to Implement

Hosted Device developer implement this interface when writing a deviceprovider.

When to use

The device host uses this interface to start and stop a device provider.The device provider is automatically started on boot up.

Methods and Properties Method Description Start Starts the deviceprovider Stop Stops the device providerIUPnPDeviceProvider::Start

The IUPnPDeviceProvider::Start method starts the device provider.HRESULT Start(   BSTR bstrInitString );

Parameters:

bstrInitString

-   -   [in] Device provider specific initialization string, which was        passed at registration.

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPnPDeviceProvider::Stop

The IUPnPDeviceProvider::Stop stops the device provider HRESULT Stop( );

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPNPEVENTSINK

The IUPnPEventSink object allows the hosted service to send eventnotifications to the device host.

IDL Reference [  uuid(204810b4-73b2-11d4-bf42-00b0d0118b56), pointer_default(unique) ] interface IUPnPEventSink: IUnknown { [helpstring(“method OnStateChanged”), hidden]  HRESULT OnStateChanged(  [in] DWORD cChanges,   [in, size_is(cChanges)] DISPID rgdispidChanges[]);  [helpstring(“method OnStateChangedSafe”)]  HRESULTOnStateChangedSafe(   [in] LONG cChanges,   [in] SAFEARRAY(DISPID)sadispidChanges); }When to ImplementUPnP Device Host implements this interface.When to useThis is the interface you must query for after the device host invokesthe Advise method on IUPnPEventSource.

Methods and Properties Method Description OnStateChanged Sends the listof variables along with their changed values to the device host fordistribution to subscribed clients. OnStateChangedSafe Used with VBclients, otherwise same functionality as IUPnPEventSink:: OnStateChangedIUPnPEventSink::OnStateChanged

The IUPnPDeviceProvider::OnStateChanged method sends an event to thedevice host with the list of DISPIDs that have changed. The device hostwill then query your service object to obtain the new values of thestate variables. This method is hidden from VB users. HRESULTOnStateChanged(  DWORD  changes,  DISPID   rgdispidChanges[ ] );Parameters:cChanges

[in] Number of variables in the list being sent to the device host.Indicates the number of variables whose value has changed.

rgdispidChanges[ ]

[in, size_is(changes)] List of DISPIDs of the state variables that havechanged.

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPnPEventSink::OnStateChangedSafe

The IUPnPDeviceProvider::OnStateChangedSafe should be used from VB, andhas the same functionality as IUPnPEventSink::OnStateChanged. HRESULTOnStateChangedSafe(   LONG cChanges   SAFEARRAY(DISPID) *rgdispidChanges);Parameters:cChanges

[in] Number of variables in the list being sent to the device host.Indicates the number of variables whose value has changed.

rgdispidChanges[ ]

[in, size_is(changes)] Safe array of DISPIDs of variables that havechanged.

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPNPEVENTSOURCE

The IUPnPEventSource interface allows the device host tosubscribe/unsubscribe to/from receiving events from the hosted service.

IDL Reference [  uuid(204810b5-73b2-11d4-bf42-00b0d0118b56), pointer_default(unique) ] interface IUPnPEventSource: IUnknown { [helpstring(“method Advise”)]  HRESULT Advise(   [in] IUnknown *punkSubscriber);  [helpstring(“method Unadvise”)]  HRESULT Unadvise(  [in] IUnknown * punkSubscriber); }When to implementService object implements if the service object has evented statevariables.When to useThe device host uses this interface to set up/tear down the associationbetween itself and the hosted service for receiving events

Methods and Properties Method Description Advise Used by the device hostto set up the association between the itself and the hosted service forthe hosted service to send events to the device host Unadvise Used bythe device host to tell the hosted service to remove the associationbetween itself and the hosted service for receiving eventsIUPnPEventSource::Advise

The IUPnPEventSource::Advise method is invoked by the device host to setup for receiving events from the hosted service. The device host passesin a pointer to its IUnknown interface that the hosted service mustquery for the IUPnPEventSink interface. HRESULT Advise(  IUnknown*punkSubscriber );Parameters:punkSubscriber

[in] Pointer to the device host's IUnknown interface that the hostedservice will query for IUPnPEventSink interface.

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPnPEventSource::Unadvise

The IUPnPEventSource::Unadvise method is invoked by the device host totell the hosted service that it does not wish to receive events. Thedevice host passes in the same object pointer that it did for theIUPnPEventSource::Advise method causing the hosted service to releasethe reference that it held. HRESULT Unadvise(  IUnknown *punkSubscriber);Parameters:punkSubscriber

[in] Pointer to the device host's IUunknown interface. This is the sameobject pointer that was passed in the IUPnPEventSource::Advise call.

Return Values:

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h.

IUPNPAUTOMATIONPROXY

The IUPnPAutomationProxy interface provides a method for executing UPnPcontrol requests by invoking a method on a service object'sservice-specific dispinterface.

IDL Definition [  object,  uuid(C4AB1FEA-D0DD-44FD-96CB-41B41B5F718A), helpstring(“IUPnPAutomationProxy Interface”),  pointer_default(unique)] interface IUPnPAutomationProxy : IUnknown {  [helpstring(“methodQueryStateVariablesByDispId”)]  HRESULT QueryStateVariablesByDispIds(  [in]  DWORD cDispIds,   [in, size_is(cDispIds)]  DISPID * rgDispIds,  [out]  DWORD * pcVariables,   [out, size_is(*pcVariables)] LPWSTR *rgszVariableNames,   [out, size_is(*pcVariables)] VARIANT * rgvarValues,  [out, size_is(*pcVariables)] LPWSTR * rgszUPnPDataTypes); [helpstring(“method ExecuteRequest”)]  HRESULT ExecuteRequest(   [in]UPNP_CONTROL_REQUEST * pucreq,   [out] UPNP_CONTROL_RESPONSE * pucresp);};When To ImplementYou should not implement this interface. The UPnP Device Host APIprovides complete functionality.When To UseThis interface will be used by the UPnP Device Host Service ControlISAPI extension.IUPnPAutomationProxy::ExecuteRequest

The IUPnPAutomationProxy::ExecuteRequest( ) method takes a deserializedcontrol request, executes the request, and returns deserialized responseinformation. HRESULT ExecuteRequest(  [in] UPNP_CONTROL_REQUEST *pucreq,  [out] UPNP_CONTROL_RESPONSE * pucresp);

Parameters

pucreq

-   -   [in] Contains a pointer to a UPNP_CONTROL_REQUEST structure        containing a deserialized UPnP control request

pucresp

-   -   [out] Contains a pointer to a caller-allocated        UPNP_CONTROL_RESPONSE structure. Upon return, this will contain        the deserialized response from the service object. Memory for        the array of output arguments will be allocated internally and        must be freed by the caller using CoTaskMemFree( ).

Return Values

If the method succeeds and the service object returns a successfulresponse to the control request, the return value is S_OK. If the methodsucceeds, but the service object returns a failure response to thecontrol request the return value is UPNP_S_ACTION_FAILED. Otherwise, themethod returns one of the COM error codes defined in WinError.h.

Remarks

If this method returns S_OK, the caller should look at the fieldspertaining to success responses in the UPnP_CONTROL_RESPONSE structurereturned. If this method returns UPnP_S_ACTION_FAILED, then the callershould look at the fields pertaining to failure responses instead.

IUPNPSERVICEDESCRIPTIONINFO

The IUPnPServiceDescriptionInfo interface provides methods for obtainingdata type information from a Service Description.

IDL Definition [  object,  uuid(f5b63656-069d-4e80-b4fd-9e0db16604d8), helpstring(“IUPnPServiceDescriptionInfo Interface”), pointer_default(unique) ] interface IUPnPServiceDescriptionInfo :IUnknown {  [helpstring(“method GetVariableType”)]  HRESULTGetVariableType(   [in] LPCWSTR pcwszVarName,   [out] BSTR * pbstrType); [helpstring(“method GetArgumentType”)]  HRESULT GetArgumentType(   [in]LPWSTR pcwszActionName,   [in] LPWSTR pcwszArgumentName,   [out] BSTR *pbstrType);  [helpstring(“method GetOutputArgumentName”)]  HRESULTGetOutputArgumentName(   [in] LPWSTR pcwszActionName,   [in] DWORDdwOutArgNum,   [out] BSTR * pbstrName); };When To ImplementYou should not implement this interface. The UPnP Device Host providescomplete functionality.When To UseThis interface will be used by the UPnP Device Host Service ControlISAPI extension and the eventing subsystem.IUPnPServiceDescriptionInfo::GetVariableType

The IUPnPServiceDescriptionInfo::GetVariableType method returns the datatype information for a service state variable. HRESULT GetVariableType( [in] LPCWSTR pcwszVarName,  [out] BSTR * pbstrType);

Parameters

pcwszVarName

-   -   [in] Contains a pointer to a null-terminated wide-character        string containing the variable name

pbstrType

-   -   [out] On successful return, receives a pointer to a BSTR that        specifies the data type of the state variable. This BSTR is        allocated internally and must be freed by the caller using        SysFreeString( ).

Return Values

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h, or one of thevalues described below:

-   -   -   UPNP_E_INVALID_VARIABLE The variable whose name is specified            by            -   pcwszVarName does not exist.

Remarks

The string returned in pbstrType contains one of the standard UPnP datatype names (e.g. “i4” or “string”).

IUPnPServiceDescriptionInfo::GetArgumentType

The IUPnPServiceDescriptionInfo::GetArgumentType method returns the datatype information for an argument to a service action. HRESULTGetArgumentType(  [in] LPWSTR pcwszActionName,  [in] LPWSTRpcwszArgumentName,  [out] BSTR * pbstrType);

Parameters

pcwszActionName

-   -   [in] Contains a pointer to a null-terminated wide-character        string containing the service action name

pcwszArgumentName

-   -   [in] Contains a pointer to a null-terminated wide-character        string containing the argument name

pbstrType

-   -   [out] On successful return, receives a pointer to a BSTR that        specifies the data type of the argument. This BSTR is allocated        internally and must be freed by the caller using SysFreeString(        ).        Return Values

If the method succeeds, the return value is S_OK. Otherwise, the methodreturns one of the COM error codes defined in WinError.h, or one of thevalues described below:

-   -   -   UPnP_E_INVALID_ACTION The action whose name is specified by            -   pcwszActionName does not exist.        -   UPnP_E_INVALID_ARGUMENT The argument whose name is specified            -   by pcwszArgumentName does not exist.

Remarks

The string returned in pbstrType contains one of the standard UPnP datatype names (e.g. “i4” or “string”).

IUPnPServiceDescriptionInfo::GetOutputArgumentName

The IUPnPServiceDescriptionInfo::GetOutputArgumentName method returnsthe name of an output argument to a service action. HRESULTGetOutputArgumentName(  [in] LPWSTR pcwszActionName,  [in] DWORDdwOutArgNum,  [out] BSTR * pbstrName);

Parameters

pcwszActionName

-   -   [in] Contains a pointer to a null-terminated wide-character        string containing the service action name

dwOutArgNum

-   -   [in] Contains the ordinal number of the output argument whose        name is being sought. This number is zero based i.e. to get the        name of the first output argument, specify 0 for this parameter;        to get the name of the second output argument, specify 1 for        this parameter etc.

pbstrName

-   -   [out] On successful return, receives a pointer to a BSTR that        contains the name of the output argument. This BSTR is allocated        internally and must be freed by the caller using SysFreeString(        ).

Return Values

-   -   If the method succeeds, the return value is S_OK. Otherwise, the        method returns one of the COM error codes defined in WinError.h,        or one of the values described below:        -   UPnP_E_INVALID_ACTION The action whose name is specified by            -   pcwszActionName does not exist.        -   UPnP_E_INVALID_ARGUMENT dwOutArgNum specifies an invalid            -   ordinal number

Appendix Universal Plug and Play Device Architecture

Table of Contents

Introduction

0. Addressing

1. Discovery

2. Description

3. Control

4. Eventing

5. Presentation

Glossary

Introduction

What is Universal Plug and Play?

Universal Plug and Play (UPnP) is an architecture for pervasivepeer-to-peer network connectivity of intelligent appliances, wirelessdevices, and PCs of all form factors. It is designed to bringeasy-to-use, flexible, standards-based connectivity to ad-hoc orunmanaged networks whether in the home, in a small business, publicspaces, or attached to the Internet. Universal Plug and Play is adistributed, open networking architecture that leverages TCP/IP and theWeb technologies to enable seamless proximity networking in addition tocontrol and data transfer among networked devices in the home, office,and public spaces.

UPnP is more than just a simple extension of the plug and playperipheral model. It is designed to support zero-configuration,“invisible” networking and automatic discovery for a breadth of devicecategories from a wide range of vendors. This means a device candynamically join a network, obtain an IP address, convey itscapabilities, and learn about the presence and capabilities of otherdevices. DHCP and DNS servers are optional and are used only ifavailable on the network. Finally, a device can leave a network smoothlyand automatically without leaving any unwanted state behind.

UPnP leverages Internet components, including IP, TCP, UDP, HTTP, andXML. Like the Internet, contracts are based on wire protocols that aredeclarative, expressed in XML, and communicated via HTTP. IPinternetworking is a strong choice for UPnP because of its provenability to span different physical media, to enable real worldmultiple-vendor interoperation, and to achieve synergy with the Internetand many home and office intranets. UPnP has been explicitly designed toaccommodate these environments. Further, via bridging, UPnP accommodatesmedia running non-IP protocols when cost, technology, or legacy preventsthe media or devices attached to it from running IP.

What is “universal” about UPnP? No device drivers; common protocols areused instead. UPnP networking is media independent. UPnP devices can beimplemented using any programming language, and on any operating system.UPnP does not specify or constrain the design of an API for applicationsrunning on control points; OS vendors may create APIs that suit theircustomer's needs. UPnP enables vendor control over device UI andinteraction using the browser as well as conventional applicationprogrammatic control.

UPnP Forum

The UPnP Forum is an industry initiative designed to enable easy androbust connectivity among stand-alone devices and PCs from manydifferent vendors. The UPnP Forum seeks to develop standards fordescribing device protocols and XML-based device schemas for the purposeof enabling device-to-device interoperability in a scalable networkedenvironment. The UPnP Forum oversees a logo program for compliantdevices.

The UPnP Forum has set up working committees in specific areas of domainexpertise. These working committees are charged with creating proposeddevice standards, building sample implementations, and buildingappropriate test suites. This document indicates specific technicaldecisions that are the purview of UPnP Forum working committees.

UPnP vendors can build compliant devices with confidence ofinteroperability and benefits of shared intellectual property and thelogo program. Separate from the logo program, vendors may also builddevices that adhere to the UPnP Device Architecture defined hereinwithout a formal standards procedure. If vendors build non-standarddevices, they determine technical decisions that would otherwise bedetermined by a UPnP Forum working committee.

In this Document

The Universal Plug and Play (UPnP) Device Architecture described hereindefines the protocols for communication between controllers, or controlpoints, and devices. For discovery, description, control, eventing, andpresentation, UPnP uses the following protocol stack.

At the highest layer, messages logically contain only UPnPvendor-specific information about their devices. Moving down the stack,vendor content is supplemented by information defined by UPnP Forumworking committees. Messages from the layers above are hosted inUPnP-specific protocols, defined in this document. In turn, the abovemessages are formatted using the Simple Service Discovery Protocol(SSDP), General Event Notification Architecture (GENA), and SimpleObject Access Protocol (SOAP). The above messages are delivered viaHTTP, either a multicast or unicast variety running over UDP, or thestandard HTTP running over TCP. Ultimately, all messages above aredelivered over IP. The remaining sections of this document describe thecontent and format for each of these protocol layers in detail. Forreference, colors in [square brackets] above indicate which protocoldefines specific message components throughout this document.

The foundation for UPnP networking is IP addressing. Each device has aDynamic Host Configuration Protocol (DHCP) client and search for a DHCPserver when the device is first connected to the network. If a DHCPserver is available, i.e., the network is managed, the device uses theIP addressed assigned to it. If no DHCP server is available, i.e., thenetwork is unmanaged, the device uses Auto IP to get an address. Inbrief, Auto IP defines how a device intelligently chooses an IP addressfrom a set of reserved addresses and is able to move easily betweenmanaged and unmanaged networks. If during the DHCP transaction, thedevice obtains a domain name, e.g., through a DNS server or via DNSforwarding, the device uses that name in subsequent network operations;otherwise, the device uses its IP address.

Given an IP address, the first step in UPnP networking is discovery.When a device is added to the network, the UPnP discovery protocolallows that device to advertise its services to control points on thenetwork. Similarly, when a control point is added to the network, theUPnP discovery protocol allows that control point to search for devicesof interest on the network. The fundamental exchange in both cases is adiscovery message containing a few, essential specifics about the deviceor one of its services, e.g., its type, identifier, and a pointer tomore detailed information. The UPnP discovery protocol is based on theSimple Service Discovery Protocol (SSDP). The section on Discovery belowexplains how devices advertise, how control points search, and detailsof the format of discovery messages.

The second step in UPnP networking is description. After a control pointhas discovered a device, the control point still knows very little aboutthe device. For the control point to learn more about the device and itscapabilities, or to interact with the device, the control pointretrieves the device's description from the URL provided by the devicein the discovery message. Devices may contain other, logical devices, aswell as functional units, or services. The UPnP description for a deviceis expressed in XML and includes vendor-specific, manufacturerinformation like the model name and number, serial number, manufacturername, URLs to vendor-specific Web sites, etc. The description alsoincludes a list of any embedded devices or services, as well as URLs forcontrol, eventing, and presentation. For each service, the descriptionincludes a list of the commands, or actions, the service responds to,and parameters, or arguments, for each action; the description for aservice also includes a list of variables; these variables model thestate of the service at run time, and are described in terms of theirdata type, range, and event characteristics. The section on Descriptionbelow explains how devices are described and how those descriptions areretrieved by control points.

The third step in UPnP networking is control. After a control point hasretrieved a description of the device, the control point can sendactions to a device's service. To do this, a control point sends asuitable control message to the URL for control URL for the service(provided in the device description). Control messages are alsoexpressed in XML using the Simple Object Access Protocol (SOAP). Likefunction calls, in response to the control message, the service returnsany action-specific values. The effects of the action, if any, aremodeled by changes in the variables that describe the run-time state ofthe service. The section on Control below explains the description ofactions, state variables, and the format of control messages.

The fourth step in UPnP networking is eventing. A UPnP description for aservice includes a list of actions the service responds to and a list ofvariables that model the state of the service at run time. The servicepublishes updates when these variables change, and a control point maysubscribe to receive this information. The service publishes updates bysending event messages. Event messages contain the names of one of morestate variables and the current value of those variables. These messagesare also expressed in XML and formatted using the General EventNotification Architecture (GENA). A special initial event message issent when a control point first subscribes; this event message containsthe names and values for all evented variables and allows the subscriberto initialize its model of the state of the service. To supportscenarios with multiple control points, eventing is designed to keep allcontrol points equally informed about the effects of any action.Therefore, all subscribers are sent all event messages, subscribersreceive event messages for all evented variables that have changed, andevent messages are sent no matter why the state variable changed (eitherin response to a requested action or because the state the service ismodeling changed). The section on Eventing below explains subscriptionand the format of event messages.

The fifth step in UPnP networking is presentation. If a device has a URLfor presentation, then the control point can retrieve a page from thisURL, load the page into a browser, and depending on the capabilities ofthe page, allow a user to control the device and/or view device status.The degree to which each of these can be accomplished depends on thespecific capabilities of the presentation page and device. The sectionon Presentation below explains the protocol for retrieving apresentation page.

0. Addressing

Addressing is Step 0 of UPnP networking. Through addressing, devices geta network address. Addressing enables discovery (Step 1) where controlpoints find interesting device(s), description (Step 2) where wherecontrol points learn about device capabilities, control (Step 3) where acontrol point sends commands to device(s), eventing (Step 4) wherecontrol points listen to state changes in device(s), and presentation(Step 5) where control points display a user interface for device(s).

The foundation for UPnP networking is IP addressing. Each device has aDynamic Host Configuration Protocol (DHCP) client and search for a DHCPserver when the device is first connected to the network. If a DHCPserver is available, i.e., the network is managed, the device uses theIP addressed assigned to it. If no DHCP server is available, i.e., thenetwork is unmanaged; the device uses automatic IP addressing (Auto-IP)to obtain an address.

Auto-IP defines how a device: (a) determines if DHCP is unavailable, and(b) intelligently chooses an IP address from a set of link-local IPaddresses. This method of address assignment enables a device to easilymove between managed and unmanaged networks.

The operations described in this section are further clarified in thereference documents listed below. Where conflicts between this documentand the reference documents exist, the reference document always takesprecedence.

0.1 Addressing: Determining Whether to use Auto-IP

A device that supports AUTO-IP and is configured for dynamic addressassignment begins by requesting an IP address via DHCP by sending out aDHCPDISCOVER message. The amount of time this DHCP Client listens forDHCPOFFERS is implementation dependent. If a DHCPOFFER is receivedduring this time, the device continues the process of dynamic addressassignment. If no valid DHCPOFFERS are received, the device may thenauto-configure an IP address.

0.2 Addressing: Choosing an Address

To auto-configure an IP address using Auto-IP, the device uses animplementation dependent algorithm for choosing an address in the169.254/16 range. The first and last 256 addresses in this range arereserved and is not used.

The selected address then is tested to determine if the address isalready in use. If the address is in use by another device, anotheraddress is chosen and tested, up to an implementation dependent numberof retries. The address selection is randomized to avoid collision whenmultiple devices are attempting to allocate addresses.

0.3 Addressing: Testing the Address

To test the chosen address, the device uses an Address ResolutionProtocol (ARP) probe. An ARP probe is an ARP request with the devicehardware address used as the sender's hardware address and the sender'sIP address set to 0s. The device will then listen for responses to theARP probe, or other ARP probes for the same IP address. If either ofthese ARP packets is seen, the device considers the address in use andtry a new address.

0.4 Addressing: Periodic Checking for Dynamic Address Availability

A device that has auto-configured an IP address periodically checks forthe existence of a DHCP server. This is accomplished by sendingDHCPDISCOVER messages. How often this check is made is implementationdependent, but checking every 5 minutes would maintain a balance betweennetwork bandwidth required and connectivity maintenance. If a DHCP offeris received, the device proceeds with dynamic address allocation. Once aDHCP assigned address is in place, the device may release theauto-configured address, but may also choose to maintain this addressfor a period of time to maintain connectivity.

To switch over from one IP address to a new one, the device cancels anyoutstanding advertisements and reissue new ones. The section onDiscovery explains advertisements and their cancellations.

0.5 Addressing: Device Naming and DNS Interaction

Once a device has a valid IP address for the network, it can be locatedand referenced on that network through that address. There may besituations where the end user needs to locate and identify a device. Inthese situations, a friendly name for the device is much easier for ahuman to use than an IP address.

Moreover, names are much more static than IP addresses. Clientsreferring a device by name don't require any modification when IPaddress of a device changes. Mapping of the device's DNS name to its IPaddress could be entered into DNS database manually or dynamicallyaccording to RFC 2136. While computers and devices supporting dynamicDNS updates can register their DNS records directly in DNS, it is alsopossible to configure a DHCP server to register DNS records on behalf ofthese DHCP clients.

0.6 Addressing: Name to IP Address Resolution

A computer that needs to contact a device identified by a DNS name needsto discover its IP address. The computer submits a DNS query accordingto RFC1034 and 1035 to the pre-configured DNS server(s) and receives aresponse from a DNS server containing the IP address of the targetdevice. A computer can be statically pre-configured with the list of DNSservers. Alternatively a computer could be configured with the list ofDNS server through DHCP, or after the address assignment through aDHCPINFORM message.

1. Discovery

Discovery is Step 1 in UPnP networking. Discovery comes after addressing(Step 0) where devices get a network address. Through discovery, controlpoints find interesting device(s). Discovery enables description (Step2) where control points learn about device capabilities, control (Step3) where a control point sends commands to device(s), eventing (Step 4)where control points listen to state changes in device(s), andpresentation (Step 5) where control points display a user interface fordevice(s).

Discovery is the first step in UPnP networking. When a device is addedto the network, the UPnP discovery protocol allows that device toadvertise its services to control points on the network. Similarly, whena control point is added to the network, the UPnP discovery protocolallows that control point to search for devices of interest on thenetwork. The fundamental exchange in both cases is a discovery messagecontaining a few, essential specifics about the device or one of itsservices, e.g., its type, identifier, and a pointer to more detailedinformation.

When a new device is added to the network, it multicasts a number ofdiscovery messages advertising its embedded devices and services. Anyinterested control point can listen to the standard multicast addressfor notifications that new capabilities are available.

Similarly, when a new control point is added to the network, itmulticasts a discovery message searching for interesting devices,services, or both. All devices listen to the standard multicast addressfor these messages and responds if any of their embedded devices orservices match the search criteria in the discovery message.

To reiterate, a control point may learn of a device of interest becausethat device sent discovery messages advertising itself or because thedevice responded to a discovery message searching for devices. In eithercase, if a control point is interested in a device and wants to learnmore about it, the control point uses the information in the discoverymessage to send a description query message. The section on Descriptionexplains description messages in detail.

When a device is removed from the network, it multicasts a number ofdiscovery messages revoking it's earlier announcements, effectivelydeclaring that it's embedded devices and services will not be available.

To limit network congestion, the time-to-live (TTL) of each IP packetfor each multicast message defaults to 4 and is configurable.

Discovery plays an important role in the interoperability of devices andcontrol points using different versions of UPnP networking. The UPnPDevice Architecture (defined herein) is versioned with both a major anda minor version, usually written as major.minor, where both major andminor are integers. Advances in minor versions is a compatible supersetof earlier minor versions of the same major version. Advances in majorversion are not required to be supersets of earlier versions and are notguaranteed to be backward compatible. Version information iscommunicated in discovery and description messages. In the former, eachdiscovery message includes the version of UPnP networking that thedevice supports. As a backup, the latter also includes the sameinformation. This section explains the format of version information indiscovery messages and specific requirements on discovery messages tomaintain compatibility with advances in minor versions.

The standard multicast address, as well as the mechanisms foradvertising, searching, and revoking, are defined by the Simple ServiceDiscovery Protocol (SSDP). The remainder of this section explains SSDPin detail, enumerating how devices advertise and revoke theiradvertisements as well as how control points search and devices respond.

1.1 Discovery: Advertisement

When a device is added to the network, the UPnP discovery protocolallows that device to advertise its services to control points. It doesthis by multicasting discovery messages to a standard address and port.Control points listen to this port to detect when new capabilities areavailable on the network. To advertise the full extent of itscapabilities, a device multicasts a number of discovery messagescorresponding to each of its embedded devices and services. Each messagecontains information specific to the embedded device (or service) aswell as information about its enclosing device. Messages includeduration until the advertisements expire; if the device remainsavailable, the advertisements are re-sent with (with new duration). Ifthe device becomes unavailable, the device explicitly cancels itsadvertisements, but if the device is unable to do this, theadvertisements will expire on their own.

1.1.1 Discovery: Advertisement Protocols and Standards

To send (and receive) advertisements, devices (and control points) usethe following subset of the overall UPnP protocol stack. (The overallUPnP protocol stack is listed at the beginning of this document.)

At the highest layer, discovery messages contain vendor-specificinformation, e.g., URL for the device description and device identifier.Moving down the stack, vendor content is supplemented by informationfrom a UPnP Forum working committee, e.g., device type. Messages fromthe layers above are hosted in UPnP-specific protocols, defined in thisdocument. In turn, the above messages are delivered via a multicastvariant of HTTP that has been extended using General Event NotificationArchitecture (GENA) methods and headers and Simple Service DiscoveryProtocol (SSDP) headers. The HTTP messages are delivered via UDP overIP. For reference, colors in [square brackets] above indicate whichprotocol defines specific headers and values in discovery messageslisted below.

1.1.2 Discovery: Advertisement: Device Available—NOTIFY with ssdp:alive

When a device is added to the network, it multicasts discovery messagesto advertise its root device, to advertise any embedded devices, and toadvertise its services. Each discovery message contains four majorcomponents:

-   -   1. a potential search target (e.g., device type) sent in an NT        header,    -   2. a composite identifier for the advertisement sent in a USN        header,    -   3. a URL for more information about the device (or enclosing        device in the case of a service) sent in a LOCATION header, and    -   4. a duration for which the advertisement is valid sent in a        CACHE-CONTROL header.

To advertise its capabilities, a device multicasts a number of discoverymessages. Specifically, a root device multicasts:

Three discovery messages for the root device. NT USN 1 device UUIDdevice UUID 2 device type device UUID and :: and device type 3upnp:rootdevice device UUID and :: and upnp:rootdevice

Two discovery messages for each embedded device. NT USN 1 device UUIDdevice UUID 2 device type device UUID and :: and device type

Once for each service. NT USN 1 service type device UUID and :: andservice type

If a root device has d embedded devices and s embedded services but onlyk distinct service types, this works out to 3+2d+k requests. Thisadvertises the full extend of the device's capabilities to interestedcontrol points. These messages are sent out as a series with roughlycomparable expiration times; order is unimportant, but refreshing orcanceling individual messages is prohibited.

Choosing an appropriate duration for advertisements is a balance betweenminimizing network traffic and maximizing freshness of device status.Relatively short durations close to the minimum of 1800 seconds willensure that control points have current device status at the expense ofadditional network traffic; longer durations, say on the order of a day,compromise freshness of device status but can significantly reducenetwork traffic. Generally, device vendors choose a value thatcorresponds to expected device usage: short durations for devices thatare expected to be part of the network for short periods of time, andsignificantly longer durations for devices expected to be long-termmembers of the network.

Due to the unreliable nature of UDP, devices send each of the abovediscovery messages more than once. As a fallback, to guard against thepossibility that a control point might not receive an advertisement fora device or service, the device re-sends its advertisements periodically(cf. CACHE-CONTROL below). Note that UDP packets are also bounded inlength (perhaps as small as 512 Bytes in some implementations) and thatthere is no guarantee that the above 3+2d+k messages will arrive in aparticular order.

When a device is added to the network, it sends a multicast request withmethod NOTIFY and ssdp:alive in the NTS header in the following format.Values in italics are placeholders for actual values.

NOTIFY * HTTP/1.1

HOST: 239.255.255.250:1900

CACHE-CONTROL: max-age=seconds until advertisement expires

LOCATION: URL for UPnP description for root device

NT: search target

NTS: ssdp:alive

SERVER: OS/version, UPnP/1.0, product/version

USN: advertisement UUID

(No body for request with method NOTIFY, but note that the message has ablank line following the last HTTP header.) The TTL for the IP packetdefaults to 4 and is configurable.

Listed below are details for the request line and headers appearing inthe listing above. All header values are case sensitive except wherenoted.

Request line

NOTIFY

Method defined by GENA for sending notifications and events.

Request applies generally and not to a specific resource.

HTTP/1.1

HTTP version.

Headers

HOST

Multicast channel and port reserved for SSDP by Internet AssignedNumbers Authority (LANA). Is 239.255.255.250:1900.

CACHE-CONTROL

max-age directive specifies number of seconds the advertisement isvalid. After this duration, control points assume the device (orservice) is no longer available. Specified by UPnP vendor. Integer.

LOCATION

Contains a URL to the UPnP description of the root device. In someunmanaged networks, host of this URL may contain an IP address (versus adomain name). Specified by UPnP vendor. Single URL.

NT

Notification Type. Is one of the following. Single URI.

unp:rootdevice

Sent once for root device.

uuid:schemas-upnp-org:device:device-type:device-UUID

Specified by UPnP vendor. Sent once for each device, root or embedded.

urn:schemas-upnp-org:device:device-type

Defined by UPnP Forum working committee. Sent once for each device, rootor embedded.

urn:schemas-upnp-org:service:service-type

Defined by UPnP Forum working committee. Sent once for each service.

NTS

Notification Sub Type. Is ssdp:alive. Single URI.

SERVER

Concatenation of OS name, OS version, UPnP/1.0, product name, andproduct version. Specified by UPnP vendor. String.

USN

header defined by SSDP. Unique Service Name. Is one of the following.(cf. table above.) The prefix (before the double colon) matches thevalue of the UDN element in the device description. (The section onDescription explains the UDN element.) Single URI.

uuid:device-UUID::upnp:rootdevice

Sent once for root device.

uuid:device-UUID

Specified by UPnP vendor. Sent once for every device, root or embedded.

uuid:device-UUID::urn:schemas-upnp-org:device:deviceType:v

Sent once for every device, root or embedded.

uuid:device-UUID::urn:schemas-upnp-org:service:serviceType:v

Sent once for every service.

(No response for a request with method NOTIFY.)

1.1.3 Discovery: Advertisement: Device Unavailable—NOTIFY withssdp:byebye

When a device and its services are going to be removed from the network,the device multicasts a ssdp:byebye message corresponding to each of thessdp:alive messages it multicasted that have not already expired. If thedevice is removed abruptly from the network, it might not be possible tomulticast a message. As a fallback, discovery messages include anexpiration value in a CACHE-CONTROL header (as explained above); if notre-advertised, the discovery message eventually expires on its own andis removed from any control point cache.

(Note: when a control point is about to be removed from the network, nodiscovery-related action is required.)

When a device is about to be removed from the network, it explicitlyrevokes its discovery messages by sending one multicast request for eachssdp:alive message it sent. Each multicast request has method NOTIFY andssdp:byebye in the NTS header in the following format. Values in italicsare placeholders for actual values. <SPAN class=gena>NOTIFY</SPAN> *HTTP/1.1 HOST: <SPAN class=ssdp>239.255.255.250</SPAN>:<SPANclass=ssdp>1900</SPAN> <SPAN class=gena>NT</SPAN>: <SPANclass=vendor>search target</ SPAN> <SPAN class=gena>NTS</SPAN>: <SPANclass=ssdp>ssdp:byebye</ SPAN> <SPAN class=ssdp>USN</SPAN>: <SPANclass=vendor>advertisement UUID</SPAN>

(No body for request with method NOTIFY, but note that the message has ablank line following the last HTTP header.) The TTL for the IP packetdefaults to 4 and is configurable.

Listed below are details for the request line and headers appearing inthe listing above. All header values are case sensitive except wherenoted.

Request line

NOTIFY

Method defined by GENA for sending notifications and events.

Request applies generally and not to a specific resource.

HTTP/1.1

HTTP version.

Headers

HOST

Multicast channel and port reserved for SSDP. Is 239.255.255.250:1900.

NT

Notification Type. Single URI.

NTS

Notification Sub Type. Is ssdp:byebye. Single URI.

USN

Unique Service Name. Single URI.

(No response for a request with method NOTIFY.)

Due to the unreliable nature of UDP, devices send each of the abovemessages more than once. As a fallback, if a control point fails toreceive notification that a device or services is unavailable, theoriginal discovery message will eventually expire yielding the sameeffect.

1.2 Discovery: Search

When a control point is added to the network, the UPnP discoveryprotocol allows that control point to search for devices of interest onthe network. It does this by multicasting a search message with apattern, or target, equal to a type or identifier for a device orservice. Responses from devices contain discovery messages essentiallyidentical to those advertised by newly connected devices; the former areunicast while the latter are multicast.

1.2.1 Discovery: Search Protocols and Standards

To search for devices (and be discovered by control points), controlpoints (and devices) use the following subset of the overall UPnPprotocol stack. (The overall UPnP protocol stack is listed at thebeginning of this document.)

At the highest layer, search messages contain vendor-specificinformation, e.g., the control point, device, and service identifiers.Moving down the stack, vendor content is supplemented by informationfrom a UPnP Forum working committee, e.g., device or service types.Messages from the layers above are hosted in UPnP-specific protocols,defined in this document. In turn, search requests are delivered via amulticast variant of HTTP that has been extended using Simple ServiceDiscovery Protocol (SSDP) methods headers. Search responses aredelivered via a unicast variant of HTTP that has also been extended withSSDP. (GENA is not involved when control points search for devices.)Both kinds of HTTP messages are delivered via UDP over IP. Forreference, colors in [square brackets] above indicate which protocoldefines specific headers and values in discovery messages listed below.

1.2.2 Discovery: Search: Request with M-SEARCH

When a control point is added to the network, it sends a multicastrequest with method M-SEARCH in the following format. Values in italicsare placeholders for actual values.

M-SEARCH * HTTP/1.1

HOST: 239.255.255.250:1900

MAN: “ssdp:discover”

MX: seconds to delay response

S: uuid:control point UUID

ST: search target

(No body for request with method M-SEARCH.)

Listed below are details for the request line and headers appearing inthe listing above. All header values are case sensitive except wherenoted.

Request line

M-SEARCH

Method defined by SSDP for search requests.

Request applies generally and not to a specific resource.

HTTP/1.1

HTTP version.

Headers

HOST

Multicast channel and port reserved for SSDP. Is 239.255.255.250:1900.

MAN

Is “ssdp:discover”.

MX

Maximum wait. Device responses are delayed a random duration between 0and this many seconds to balance load for the control point when itprocesses responses. Specified by UPnP vendor. Integer.

S

Source identifier. Universally-unique identifier for the control point.Specified by UPnP vendor. Single URI.

ST

Search Target. Is one of the following. (cf. NT header inadvertisement.) Single URI.

ssdp:all

Search for all devices and services.

upnp:rootdevice

Search for root devices only.

uuid:schemas-upnp-org:device:device-type:device-UUID

Specified by UPnP vendor. Search for a particular device.

urn:schemas-upnp-org:device:device-type

Defined by UPnP Forum working committee. Search for any device of thistype.

urn:schemas-upnp-org:service:service-type

Defined by UPnP Forum working committee. Search for any service of thistype.

1.2.3 Discovery: Search: Response

To be found, a device sends a response in the following format. (Compareto multicast request with method NOTIFY and ssdp:alive in the NTS headerabove.) Values in italics are placeholders for actual values.

HTTP/1.1 200 OK

CACHE-CONTROL: max-age=seconds until advertisement expires

DATE: when response was generated

EXT:

LOCATION: URL for UPnP description for root device

S: uuid:control point UUID

SERVER: OS/version, UPnP/1.0, product/version

ST: search target

USN: uuid:schemas-upnp-org:device:device-type:UUID

(No body for a response to a request with method M-SEARCH.)

Listed below are details for the headers appearing in the listing above.All header values are case sensitive except where noted.

Headers

CACHE-CONTROL

max-age directive specifies number of seconds the advertisement isvalid. After this duration, control points assume the device (orservice) is no longer available. Specified by UPnP vendor. Integer.

DATE

When response was generated. RFC 1123 date.

EXT

Confirms that the MAN header was understood. (Header only; no value.)

LOCATION

Contains a URL to the UPnP description of the root device. Specified byUPnP vendor. Single URL.

S

Source identifier. Is the universally-unique identifier sent in therequest. Specified by UPnP vendor. Single URI.

SERVER

Concatenation of OS name, OS version, UPnP/1.0, product name, andproduct version. Specified by UPnP vendor. String.

ST

Search Target. Single URI. If ST header in request was,

ssdp:all

Respond 3+2d+s times for a root device with d embedded devices and sembedded services.

upnp:rootdevice

Respond once for root device.

uuid:schemas-upnp-org:device:device-type:device-UUID

Respond once for each device, root or embedded.

urn:schemas-upnp-org:device:device-type

Respond once for each device, root or embedded.

urn:schemas-upnp-org:service:service-type

Respond once for each service.

USN

Unique Service Name. Single URI.

(No UPnP-specific errors are defined for search messages.) Errors may bereturned by layers in the protocol stack below UPnP. Consultdocumentation on those protocols for details.

2. Description

Description is Step 2 in UPnP networking. Description comes afterdiscovery (Step 1) where control points find interesting device(s). Anddescription enables control (Step 3) where a control points sendcommands to device(s), eventing (Step 4) where control points listen tostate changes in device(s), and presentation (Step 5) where controlpoints display a user interface for device(s).

After a control point has discovered a device, the control point stillknows very little about the device—only the information that was in thediscovery message, i.e., the device's (or service's) UPnP type, thedevice's universally-unique identifier, and a URL to the device's UPnPdescription. For the control point to learn more about the device andits capabilities, or to interact with the device, the control pointretrieves the device's description from the URL provided by the devicein the discovery message.

The UPnP description for a device includes vendor-specific, manufacturerinformation like the model name and number, serial number, manufacturername, URLs to vendor-specific Web sites, etc. (details below). Thedescription also includes a list of any embedded devices or services, aswell as URLs for control, eventing, and presentation. This sectionexplains embedded devices; the section on Control explains how servicesare described, and the sections on Control, Eventing, and Presentationexplain how URLs for control, eventing, and presentation are used,respectively.

Note that a single physical device may include multiple logical devices.Multiple logical devices can be modeled as a single root device withembedded devices (and services) or as multiple root devices (perhapswith no embedded devices). In either case, there is one UPnP descriptionfor each root device, with embedded device descriptions as needed.

The UPnP description for a device is written by a UPnP vendor. Thedescription is in XML syntax and is usually based on a standard UPnPDevice Template. A UPnP Device Template is produced by a UPnP Forumworking committee; they derive the template from the UPnP TemplateLanguage, which was derived from standard constructions in XML. Thissection explains the format for a UPnP device description, UPnP DeviceTemplates, and the part of the UPnP Template Language that coversdevices. (The section on Control explains the part of the UPnP TemplateLanguage that covers services.)

Retrieving the UPnP description for a device is simple: the controlpoint issues an HTTP GET request on the URL in the discovery message,and the device returns the description document. The protocol stack,method, headers, and body for the response and request are explained indetail below.

UPnP vendors can differentiate their devices by extending services,including additional UPnP services, or embedding additional UPnPdevices. When a control point retrieves a particular device'sdescription, these added features are exposed to the control point forcontrol, eventing, and presentation. (Other means for UPnP vendordifferentiation are explained in the control section.)

The remainder of this section first explains how devices are described,explaining details of vendor-specific information, embedded devices, andURLs for control, eventing, and presentation. Then it explains UPnPDevice Templates and the UPnP Template Language as it pertains todescribing devices. Finally, it explains in detail how a control pointretrieves a description from a device.

2.1 Description: Device Description

The UPnP description for a device contains several pieces ofvendor-specific information, definitions of embedded devices andservices, and URLs for control, eventing, and presentation of thedevice.

To illustrate these, below is a listing with placeholders (in italics)for actual elements and values. Some of these placeholders would bespecified by a UPnP Forum working committee (colored red) or by a UPnPvendor (purple). (Elements defined by the UPnP Device Architecture arecolored green for later reference.) Immediately following the listing isa detailed explanation of the elements, attributes, and values. <?xmlversion=“1.0”?> <root xmlns=“urn:schemas-upnp-org:device:1:0”><specVersion> <major>1</major> <minor>0</minor> </specVersion><URLBase>base URL for all relative URLs</URLBase> <device><deviceType>urn:schemas-upnp-org:device:device-type</deviceType><friendlyName>short user-friendly title</friendlyName><modelDescription>long user-friendly title</modelDescription><modelName>model name</modelName> <modelNumber>modelnumber</modelNumber> <modelURL>URL to model site</modelURL><manufacturer>manufacturer name</manufacturer> <manufacturerURL>URL tomanufacturer site</manufacturerURL> <serialNumber>manufacturer's serialnumber</serialNumber><UDN>uuid:schemas-upnp-org:device:device-type:UUID</UDN> <UPC>UniversalProduct Code</UPC> <iconList> <icon> <mimetype>image/format</mimetype><width>horizontal pixels</width> <height>vertical pixels</height><depth>color depth</depth> <url>URL to icon</url> </icon> XML to declareother icons, if any, go here </iconList> <serviceList> <service><serviceType> urn:schemas-upnp-org:service:service-type:service-version</serviceType> <serviceId>service ID</serviceId> <SCPDURL>URL to servicedescription</SCPDURL> <controlURL>URL for control</controlURL><eventSubURL>URL for eventing</eventSubURL> </service> Declarations forother services defined by a UPnP Forum working committee (if any) gohere Declarations for other services added by UPnP vendor (if any) gohere </serviceList> <deviceList> Description of embedded devices definedby a UPnP Forum working committee (if any) go here Description ofembedded devices added by UPnP vendor (if any) go here </deviceList><presentationURL>URL for presentation</presentationURL> </device></root>

Listed below are details for each of the elements, attributes, andvalues appearing in the listing above. All elements and attributes arecase sensitive; HTTP specifies case sensitivity for URLs; other valuesare not case sensitive except where noted. The order of elements isinsignificant.

xml

Case sensitive.

root

Has urn:schemas-upnp-org:device:1:0 as the value for the xmlnsattribute; this references the UPnP Template Language (described below).Case sensitive. Contains all other elements describing the root device,i.e., contains the following sub elements:

specVersion

Contains the following sub elements:

major

Major version of the UPnP Device Architecture. Is 1.

minor

Minor version of the UPnP Device Architecture. Is 0.

URLBase

Defines the base URL. Used to construct fully-qualified URLs. Allrelative URLs that appear elsewhere in the description are appended tothis base URL. If URLBase is empty or not given, the base URL is thevalue of the LOCATION header in the discovery message. Specified by UPnPvendor. Single URL.

device

Contains the following sub elements:

deviceType

UPnP device type.

-   -   For standard devices defined by a UPnP Forum working committee,        begins with urn:schemas-upnp-org:device: followed by a device        type suffix (as shown in the listing above).    -   For non-standard devices specified by UPnP vendors, begins with        urn:, followed by a domain name owned by the vendor, followed by        :device:, followed by a device type suffix, i.e.,        urn:domain-name:device:device-type.

Single URI.

friendlyName

Short description for end user. Is localized (cf. ACCEPT-LANGUAGEheader). String. Is <64 characters.

manufacturer

Manufacturer's name. Specified by UPnP vendor. String. Is <64characters.

manufacturerURL

Web site for Manufacturer. May be relative to base URL. Specified byUPnP vendor. Single URL.

modelDescription

Long description for end user. Is localized (cf. ACCEPT-LANGUAGEheader). Specified by UPnP vendor. String. Is <128 characters.

modelName

Model name. Specified by UPnP vendor. String. Is <32 characters.

modelNumber

Model number. Specified by UPnP vendor. String. Is <32 characters.

modelURL

Web site for model. May be relative to base URL. Specified by UPnPvendor. Single URL.

presentationURL

URL to presentation hosted by device (cf. section on Presentation). Maybe relative to base URL. Specified by UPnP vendor. Single URL.

serialNumber

Serial number. Specified by UPnP vendor. String. Is <64 characters.

UDN

Universal Device Name. Universally-unique identifier for the device,whether root or embedded.

-   -   For standard devices defined by a UPnP Forum working committee,        begins with uuid:schemas-upnp-org:device: followed by the device        type, colon; UPnP vendor specifies UUID suffix (as shown in the        listing above).    -   For non-standard devices specified by UPnP vendors, begins with        uuid:, followed by a domain name owned by the vendor, followed        by :device:, followed by the device type, colon, followed by a        UUID suffix, i.e., uuid:domain-name:device:device-type:UUID.

Single URI.

UPC

Universal Product Code. 12-digit, all-numeric code that identifies theconsumer package. Managed by the Uniform Code Council. Single UPC.

iconList

Contains the following sub elements:

icon

Icon to depict device in a control point UI. Recommend one icon in eachof the following sizes (width×height×depth): 16×16×1, 16×16×8, 32×32×1,32×32×8, 48×48×1, 48×48×8. Contains the following sub elements:

mimetype

Icon's MIME type (cf. RFC 2387). Single MIME image type.

width

Horizontal dimension of icon in pixels. Integer.

height

Vertical dimension of icon in pixels. Integer.

depth

Number of color bits per pixel. Integer.

url

-   -   Pointer to icon image. (XML does not support embedding of binary        data. See note below.) Retrieved via HTTP. May be relative to        base URL. Specified by UPnP vendor. Single URL.        serviceList

Contains the following sub elements:

service

Repeated once for each service defined by a UPnP Forum workingcommittee. If UPnP vendor differentiates device by adding additional,standard UPnP services, repeated once for additional service. Containsthe following sub elements:

controlURL

URL for control (cf. section on Control). May be relative to base URL.Specified by UPnP vendor. Single URL.

eventSubURL

URL for eventing (cf. section on Eventing). May be relative to base URL.Specified by UPnP vendor. Single URL.

SCPDURL

URL for service description (nee Service Control Protocol DefinitionURL). (cf. section on Control.) May be relative to base URL. Specifiedby UPnP vendor. Single URL.

serviceId

Service identifier. Is unique within this device description. <formatTBD>. Defined by a UPnP Forum working committee. Single URI.

serviceType

UPnP service type.

-   -   For standard service types defined by a UPnP Forum working        committee, begins with urn:schemas-upnp-org:service: followed by        a service type suffix (as shown in the listing above).    -   For non-standard service types specified by UPnP vendors, begins        with urn:, followed by a domain name owned by the vendor,        followed by :service:, followed by a service type suffix, i.e.,        urn:domain-name:service:service-type:service-version.        Single URI.        deviceList

Contains the following sub elements:

device

Repeat once for each embedded device defined by a UPnP Forum workingcommittee. If UPnP vendor differentiates device by embedding additionalUPnP devices, repeat once for each embedded device. Contains subelements as defined above for root sub element device.

For future extensibility, when processing XML like the listing above,devices and control points ignore any unknown elements and any subelements or content as specified by the Flexible XML Processing Profile(FXPP).

XML does not support directly embedding binary data, e.g., icons in UPnPdescriptions. Binary data may be converted into text (and therebyembedded into XML) using an XML data type of either bin.base64 (aMIME-style base 64 encoding for binary data) or bin.hex (hexadecimaldigits represent octets). Alternatively, the data can be passedindirectly, as it were, by embedding a URL in the XML and transferringthe data in response to a separate HTTP request; the icon(s) in UPnPdescriptions are transferred in this latter manner.

2.2 Description: UPnP Device Template

The listing above also illustrates the relationship between a UPnPdevice description and a UPnP Device Template. As explained above, theUPnP description for a device is written by a UPnP vendor, in XML,following a UPnP Device Template. A UPnP Device Template is produced bya UPnP Forum working committee as a means to standardize devices.

By appropriate specification of placeholders, the listing above can beeither a UPnP Device Template or a UPnP device description. Recall thatsome placeholders would be defined by a UPnP Forum working committee(colored red), i.e., the UPnP device type identifier, UPnP services, andUPnP embedded devices (if any). If these were defined, the listing wouldbe a UPnP Device Template, codifying the standard for this type ofdevice. UPnP Device Templates are one of the key deliverables from UPnPForum working committees.

Taking this another step further, the remaining placeholders in thelisting above would be specified by a UPnP vendor (colored purple),i.e., vendor-specific information. If these placeholders were specified(as well as the others), the listing would be a UPnP device description,suitable to be delivered to a control point to enable control, eventing,and presentation.

Put another way, the UPnP Device Template defines the overall type ofdevice, and each UPnP device description instantiates that template withvendor-specific information. The first is created by a UPnP Forumworking committee; the latter, by a UPnP vendor.

2.3 Description: UPnP Template Language for Devices

The paragraphs above explain UPnP device descriptions and illustrate howone would be instantiated from a UPnP Device Template. As explained,UPnP Device Templates are produced by UPnP Forum working committees, andthese templates are derived from the UPnP Template Language. Thistemplate language defines well-formed templates for devices andservices. Below is a listing and explanation of this language as itpertains to devices. The section on Control explains the UPnP TemplateLanguage as it pertains to services.

The UPnP Template Language is written in XML syntax and is derived fromXML Schema (Part 1: Structures, Part 2: Datatypes). XML Schema providesa set of XML constructions that express language concepts like requiredvs. optional elements, element nesting, and data types for values (aswell as other properties not of interest here). The UPnP TemplateLanguage uses these XML Schema constructions to define elements likespecVersion, URLBase, deviceType, et al listed in detail above. Becausethe UPnP Template Language is constructed using another, preciselanguage, it is unambiguous. And because the UPnP Template Language,UPnP Device Templates, and UPnP device descriptions are allmachine-readable, automated tools can automatically check to ensure thelatter two have all required elements, are correctly nested, and havevalues of the correct data types.

Below is the UPnP Template Language for devices as defined by the UPnPDevice Architecture herein. The elements it defines are used in UPnPDevice Templates; they are colored green here, and they are coloredgreen in the listing above. Below is where these elements are defined;above is where they are used.

Immediately following this is a brief explanation of the XML Schemaelements, attributes, and values used. The reference to XML Schema atthe end of the section has further details.

UPnP Template Language for Devices <?xml version=“1.0” ?> <Schemaname=“urn:schemas-upnp-org:device:1:0”xmlns=“urn:schemas-microsoft-com:xml-data”xmlns:dt=“urn:schemas-microsoft-com:datatypes”> <ElementType name=“root”content=“eltOnly”> <element type=“specVersion” /> <elementtype=“URLBase” minOccurs=“0” /> <element type=“device” /> </ElementType><ElementType name=“specVersion”> <element type=“major” /> <elementtype=“minor” /> </ElementType> <ElementType name=“major” dt:type=“int”/> <ElementType name=“minor” dt:type=“int” /> <ElementTypename=“URLBase” dt:type=“uri” /> <ElementType name=“device”content=“eltOnly”> <element type=“UDN” /> <element type=“friendlyName”/> <element type=“deviceType” /> <element type=“presentationURL”minOccurs=“0” /> <element type=“manufacturer” /> <elementtype=“manufacturerURL” minOccurs=“0” /> <element type=“modelName” /><element type=“modelNumber” minOccurs=“0” /> <elementtype=“modelDescription” minOccurs=“0” /> <element type=“modelURL”minOccurs=“0” /> <element type=“UPC” minOccurs=“0” /> <elementtype=“serialNumber” minOccurs=“0” /> <element type=“iconList” /><element type=“serviceList” /> <element type=“deviceList” minOccurs=“0”/> </ElementType> <ElementType name=“UDN” dt:type=“uri” /> <ElementTypename=“friendlyName” dt:type=“string” /> <ElementType name=“deviceType”dt:type=“uri” /> <ElementType name=“presentationURL” dt:type=“uri” /><ElementType name=“manufacturer” dt:type=“string” /> <ElementTypename=“manufacturerURL” dt:type=“uri” /> <ElementType name=“modelName”dt:type=“string” /> <ElementType name=“modelNumber” dt:type=“string” /><ElementType name=“modelDescription” dt:type=“string” /> <ElementTypename=“modelURL” dt:type=“uri” /> <ElementType name=“UPC”dt:type=“string” /> <ElementType name=“serialNumber” dt:type=“string” /><ElementType name=“iconList” content=“eltOnly”> <element type=“icon”maxOccurs=“*” /> </ElementType> <ElementType name=“icon”content=“eltOnly”> <element type=“mimetype” /> <element type=“width” /><element type=“height” /> <element type=“depth” /> <element type=“url”/> </ElementType> <ElementType name=“mimetype” dt:type=“string” /><ElementType name=“width” dt:type=“int” /> <ElementType name=“height”dt:type=“int” /> <ElementType name=“depth” dt:type=“int” /> <ElementTypename=“url” dt:type=“uri” /> <ElementType name=“deviceList”content=“eltOnly”> <element type=“device” maxOccurs=“*” /></ElementType> <ElementType name=“serviceList” content=“eltOnly”><element type=“service” maxOccurs=“*” /> </ElementType> <ElementTypename=“service” content=“eltOnly”> <element type=“serviceType” /><element type=“serviceId” /> <element type=“controlURL” /> <elementtype=“eventSubURL” /> <element type=“SCPDURL” /> </ElementType><ElementType name=“serviceType” dt:type=“uri” /> <ElementTypename=“serviceId” dt:type=“uri” /> <ElementType name=“controlURL”dt:type=“uri” /> <ElementType name=“eventSubURL” dt:type=“uri” /><ElementType name=“SCPDURL” dt:type=“uri” /> </Schema>ElementType

Defines an element in the new, derived language name attribute defineselement name. dt:type attribute defines the data type for the value ofelement in the new, derived language.

element

References an element for the purposes of declaring nesting. minOccursattribute defines minimum number of times the element occurs; default isminOccurs=1; optional elements have minOccurs=0. maxOccurs attributedefines maximum number of times the element occurs; default ismaxOccurs=1; elements that can appear one or more times havemaxOccurs=*.

2.4 Description: Retrieving a Description

As explained above, after a control point has discovered a device, itstill knows very little about the device. To learn more about the deviceand its capabilities, the control point retrieves the UPnP descriptionfor the device using the URL provided by the device in the discoverymessage. This is a simple HTTP-based process and uses the followingsubset of the overall UPnP protocol stack. (The overall UPnP protocolstack is listed at the beginning of this document.)

At the highest layer, description messages contain vendor-specificinformation, e.g., device type, service type, and services. Moving downthe stack, vendor content is supplemented by information from a UPnPForum working committee, e.g., model name, model number, and specificURLs. Messages from the layers above are hosted in UPnP-specificprotocols, defined in this document. In turn, the above messages aredelivered via HTTP over TCP over IP. For reference, colors in [squarebrackets] above indicate which protocol defines specific header and bodyelements in the description messages listed below.

Using this protocol stack, retrieving the UPnP description for a deviceis simple: the control point issues an HTTP GET request to the URL inthe discovery message, and the device returns its description in thebody of an HTTP response. The headers and body for the response andrequest are explained in detail below.

First, a control point sends a request with method GET in the followingformat. Values in italics are placeholders for actual values.

GET path to device description HTTP/1.1

HOST: host for device description port for device description

ACCEPT-LANGUAGE: language preferred by control point

(No message body for request to retrieve a description.)

Listed below are details for the request line and headers appearing inthe listing above. All header values are case sensitive except wherenoted.

Request line

GET

Method defined by HTTP.

path to device description

Path component of device description URL (LOCATION header in discoverymessage). Single, relative URL.

HTTP/1.1

HTTP version.

Headers

HOST

Domain name or IP address and optional port components of devicedescription URL (LOCATION header in discovery message). If the port isempty or not given, port 80 is assumed.

ACCEPT-LANGUAGE

Preferred language(s) for device description. If no description isavailable in this language, device may return a description in a defaultlanguage. RFC 1766 language tag(s).

After a control point sends a request, the device takes the second step:a device sends a response in the following format. Values in italics areplaceholders for actual values.

HTTP/1.1 200 OK

CONTENT-LENGTH: bytes in body

CONTENT-TYPE: text/xml

DATE: when responded

SERVER: OS/version, UPnP/1.0, product/version

The body of this response is a UPnP device description as explained indetail above.

Listed below are details for the headers appearing in the listing above.All header values are case sensitive except where noted.

Headers

CONTENT-LENGTH

Length of body in bytes. Integer.

CONTENT-TYPE

Is text/xml.

DATE

When response was generated. RFC 1123 date.

SERVER

Concatenation of OS name, slash, OS version, UPnP/1.0, product name,slash, and product version. String.

3. Control

Control is Step 3 in UPnP networking. Control comes after discovery(Step 1) where control points find interesting device(s), and afterdescription (Step 2) where control points learn about devicecapabilities. Control is intimately linked with eventing (Step 4) wherecontrol points listen to state changes in device(s). Through control,control points send actions to devices and poll for values. Control andeventing are complementary to presentation (Step 5) where control pointsdisplay a user interface provided by device(s).

After a control point has (1) discovered a device and (2) retrieved adescription of the device, the control point has the bare essentials fordevice control. To learn more about the service, a control pointretrieves a detailed UPnP description for each service.

A UPnP description for a service includes a list of the commands, oractions, the service responds to, and parameters, or arguments, for eachaction. A service description also includes a list of variables. Thesevariables model the state of the service at run time, and are describedin terms of their data type, range, and event characteristics. Thissection explains the description of actions, arguments, state variables,and properties of those variables. The section on Eventing explainsevent characteristics.

Like the UPnP description for a device, the UPnP description for aservice is written by a UPnP vendor. The description is in XML syntaxand is based on a standard UPnP Service Template. A UPnP ServiceTemplate is produced by a UPnP Forum working committee; they derive thetemplate from the UPnP Template Language, augmenting it with humanlanguage where necessary. As explained above, the UPnP Template Languageis derived from standard constructions in XML. This section explains theformat for a UPnP service description, UPnP Service Templates, typicalaugmentations in human language, and the part of the UPnP TemplateLanguage that covers services. (The section on Description explains thepart of the UPnP Template Language that covers devices.)

To control a device, a control point requests a device's service toperform an action. To do this, a control point sends a suitable controlmessage to the control URL for the service (provided in the devicedescription). In response, the service provides a simpleacknowledgement; unlike function calls, no service-specific value isreturned. The effects of the action, if any, are modeled by changes inthe variables that describe the run-time state of the service. Whenthese state variables change, events are published to all interestedcontrol points. This section explains the protocol stack for, and formatof, control messages. The section on Eventing explains eventpublication.

To prevent a race condition between events headed for control points andrequested actions headed for a service, control messages may include akey. With each new event message a service generates, the serviceincrements the key, and includes that key in the event message. When acontrol point sends a control message, it may choose to include a key.If a control message includes a key, the service checks to see if thekey is current, i.e., if no events have been sent since this key wasissued. If the key is current (or if there was no key in the controlmessage), then the service acknowledges the action request. If the keyis not current, the service fails the action request. This sectionbriefly explains the event key. The section on Eventing explains indetail event messages and event publication.

To determine the current value of a state variable, a control point maypoll the service. Similar to requesting an action, a control point sendsa suitable query message to the control URL for the service. Inresponse, the service provides the value of the variable. This sectionalso explains the format of these query messages. The section oneventing explains automatic notification of variable values.

The remainder of this section first explains how services are described,explaining details of actions, arguments, state variables, andproperties of those variables. Second, it explains UPnP ServiceTemplates, typical ways to augment service descriptions with humanlanguage, and the UPnP Template Language as it pertains to services.Third, it explains how a control point retrieves a service description.Finally, this section explains in detail how control and query messagesare formatted and sent to devices.

3.1 Control: Service Description

The UPnP description for a service defines actions and their arguments,and state variables and their data type, range, and eventcharacteristics.

Each action may have zero or more arguments. Each argument correspondsto a state variable. This direct-manipulation programming modelreinforces simplicity.

To illustrate these points, below is a listing with placeholders (initalics) for actual elements and values. For a standard UPnP service,some of these placeholders would be defined by a UPnP Forum workingcommittee (colored red) or specified by a UPnP vendor (purple). For avendor-unique service, all of these placeholders would be specified by aUPnP vendor. (Elements defined by the UPnP Device Architecture arecolored green for later reference.) Immediately following the listing isa detailed explanation of the elements, attributes, and values. <?xmlversion=“1.0”?> <scpd xmlns=“urn:schemas-upnp-org:service:1:0”><actionList> <action> <name>action name</name> <argumentList> <argument><name>formal parameter name</name> <relatedStateVariable>state variablename</relatedStateVariable> </argument> Declarations for other argumentsdefined by UPnP Forum working committee (if any) go here </argumentList></action> Declarations for other actions defined by UPnP Forum workingcommittee (if any) go here Declarations for other actions added by UPnPvendor (if any) go here </actionList> <serviceStateTable><stateVariable> <name>variable name</name> <dataType>variable datatype</dataType> <defaultValue>default value</defaultValue><allowedValueRange> <minimum>minimum value</minimum> <maximum>maximumvalue</maximum> <step>increment value</step> </allowedValueRange></stateVariable> Declarations for other state variables defined by UPnPForum working committee (if any) go here Declarations for other statevariables added by UPnP vendor (if any) go here </serviceStateTable></scpd>

Listed below are details for each of the elements, attributes, andvalues appearing in the listing above. All elements and attributes arecase sensitive; values are not case sensitive except where noted. Exceptwhere noted, the order of elements is insignificant.

xml

Case sensitive.

scpd

Has urn:schemas-upnp-org:service:1:0 as the value for the xmlnsattribute; this references the UPnP Template Language (explained below).Case sensitive. Contains all other elements describing the service,i.e., contains the following sub elements:

actionList

Contains the following sub elements:

action

Contains the following sub elements:

name

Name of action. String. Is <32 characters.

argumentList

Repeat once for each parameter. Contains the following sub elements:

argument

Contains the following sub elements:

name

Name of formal parameter. Is name of a state variable that models aneffect the action causes. String. Is <32 characters.

relatedStateVariable

Is the name of a state variable.

serviceStateTable

Contains the following sub elements:

stateVariable

If UPnP vendor differentiates service by adding additional statevariables, required for each additional variable. sendEvents attributedefines whether event messages will be generated when the value of thisstate variable changes; non-evented state variables have sendEvents=no;default is sendEvents=yes. Contains the following sub elements:

name

Name of state variable. Defined by a UPnP Forum working committee forstandard state variables; specified by UPnP vendor for extensions.String. Is <32 characters.

dataType

Defined by a UPnP Forum working committee for standard state variables;specified by UPnP vendor for extensions. Is one of the following values:

i4

Fixed point, integer number. May have a leading sign. May have leadingzeros. (No currency symbol.) (No grouping of digits to the left of thedecimal, e.g., no commas.) Is between −2147483648 and 2147483647, i.e.,4 byte, long integer. (Same as i4 data type defined by XML Schema, Part2: Datatypes.)

r8

Floating point number. Mantissa (left of the decimal) and/or exponentmay have a leading sign. Mantissa and/or exponent may have leadingzeros. Decimal character in mantissa is a period, i.e., whole digits inmantissa separated from fractional digits by period. Mantissa separatedfrom exponent by E. (No currency symbol.) (No grouping of digits in themantissa, e.g., no commas.) Is between −1.79769313486232E308 and−4.94065645841247E-324 for negative values, and between4.94065645841247E-324 and 1.79769313486232E308 for positive values,i.e., IEEE 64-bit (8-byte) double. (Same as r8 data type defined by XMLSchema, Part 2: Datatypes).

string

Unicode string. (Same as string data type defined by XML.)

dateTime

Date and Time in ISO 8601 format (Same as dateTime data type defined byXML Schema, Part 2: Datatypes.)

boolean

0, false, or no for false; 1, true, or yes for true. (Same as booleandata type defined by XML Schema, Part 2: Datatypes.)

bin.hex or bin.bin64

Hexadecimal representation of binary data. (Same as bin.base64 andbin.hex data types defined by XML Schema, Part 2: Datatypes.)

defaultValue

Expected, initial value. Defined by a UPnP Forum working committee ordelegated to UPnP vendor. Matches data type. Satisfies allowedValueListor allowedValueRange constraints.

allowedValueList

Enumerates legal string values. Prohibited for data types other thanstring. At most one of allowedValueRange and allowedValueList may bespecified. Sub elements are ordered (e.g., see NEXT_STRING_BOUNDED).Contains the following sub elements:

allowedValue

A legal value for a string variable. Defined by a UPnP Forum workingcommittee for standard state variables; specified by UPnP vendor forextensions. String. Is <32 characters.

allowedValueRange

Defines bounds for legal numeric values; defines resolution for numericvalues. Prohibited for data types other than i4 and r8. At most one ofallowedValueRange and allowedValueList may be specified. At least one ofthe following sub elements is included. Contains the following subelements:

minimum

Inclusive lower bound. Defined by a UPnP Forum working committee ordelegated to UPnP vendor. Single i4 or r8.

maximum

Inclusive upper bound. Defined by a UPnP Forum working committee ordelegated to UPnP vendor. Single i4 or r8.

step

Size of an increment operation, i.e., value of s in the operation v=v+s.Defined by a UPnP Forum working committee or delegated to UPnP vendor.Single i4 or r8.

For future extensibility, when processing XML like the listing above,devices and control points ignores any unknown elements and any subelements or content as specified by the Flexible XML Processing Profile(FXPP).

Note that it is logically possible for a service to have no actions buthave state variables and eventing; such a service would be an autonomousinformation source. Conversely, it is also logically possible for aservice to have no state variables (and no eventing) but have actions;such a service might be stateless and cause short-term environmentaleffects.

Services standardized by UPnP Forum working committees are versioned.Every later version of a service is a superset of the previous version,i.e., it includes all actions and state variables exactly as they aredefined by earlier versions of the service. The UPnP service typeremains the same across all versions of a service whereas the serviceversion is larger for later versions.

3.2 Control: UPnP Service Template

The listing above also illustrates the relationship between a UPnPservice description and a UPnP Service Template. As explained above, theUPnP description for a service is written by a UPnP vendor, in XML,following a UPnP Service Template. A UPnP Service Template is producedby a UPnP Forum working committee as a means to standardize devices.

By appropriate specification of placeholders, the listing above can beeither a UPnP Service Template or a UPnP service description. Recallthat some placeholders would be defined by a UPnP Forum workingcommittee (colored red), i.e., actions and their parameters, and statesand their data type, range, and event characteristics. If these werespecified, the listing above would be a UPnP Service Template, codifyingthe standard for this type of service. Along with UPnP Device Templates(cf. section on Description), UPnP Service Templates are one of the keydeliverables from UPnP Forum working committees.

Taking this another step further, the remaining placeholders in thelisting above would be specified by a UPnP vendor (colored purple),i.e., additional, vendor-specified actions and state variables. If theseplaceholders were specified (as well as the others), the listing wouldbe a UPnP service description, suitable for effective control of theservice within a device.

Put another way, the UPnP Service Template defines the overall type ofservice, and each UPnP service description instantiates that templatewith vendor-specific additions. The first is created by a UPnP Forumworking committee; the latter, by a UPnP vendor.

3.3 Control: UPnP Template Language for Services

The paragraphs above explain UPnP service descriptions and illustratehow one would be instantiated from a UPnP Service Template. Like UPnPDevice Templates, UPnP Service Templates are produced by UPnP Forumworking committees, and these templates are derived from the UPnPTemplate Language. This template language defines well-formed templatesfor devices and services. The section on Description explains the UPnPTemplate Language as it pertains to devices. As explained in the sectionon Description, the UPnP Template Language is written in XML syntax andis derived from XML Schema (Part 1: Structures, Part 2: Datatypes).Below is a listing of this language as it pertains to services. Theelements it defines are used in UPnP Service Templates; they are coloredgreen here, and they are colored green in the listing above. Below iswhere these elements are defined; above is where they are used.

Immediately following this is a brief explanation of the XML Schemaelements, attributes, and values used. The reference to XML Schema atthe end of the section has further details.

UPnP Template Language for Services <?xml version=“1.0”?> <Schemaname=“urn:schemas-upnp-org:service:1:0”xmlns=“urn:schemas-microsoft-com:xml-data”xmlns:dt=“urn:schemas-microsoft-com:datatypes”> <ElementType name=“name”content=“textOnly” dt:type=“string” /> <ElementType name=“defaultValue”content=“textOnly” dt:type=“string” /> <ElementType name=“minimum”content=“textOnly” dt:type=“number” /> <ElementType name=“maximum”content=“textOnly” dt:type=“number” /> <ElementType name=“step”content=“textOnly” dt:type=“number” /> <ElementTypename=“allowedValueRange” content=“eltOnly” model=“closed”> <elementtype=“minimum” /> <element type=“maximum” /> <element type=“step”minOccurs=“0” /> </ElementType> <ElementType name=“allowedValue”content=“textOnly” /> <ElementType name=“allowedValueList”content=“eltOnly” model=“closed”> <element type=“allowedValue”minOccurs=“1” maxOccurs=“*” /> </ElementType> <ElementTypename=“dataType” content=“textOnly” dt:type=“string” /> <ElementTypename=“stateVariable” content=“eltOnly” model=“closed”> <elementtype=“name” /> <element type=“dataType” /> <element type=“defaultValue”minOccurs=“0” maxOccurs=“1” /> <group minOccurs=“0” maxOccurs=“1”order=“one”> <element type=“allowedValueList” /> <elementtype=“allowedValueRange” /> </group> <AttributeType name=“sendEvents” /><attribute default=“yes” type=“sendEvents” required=“no” /></ElementType> <ElementType name=“serviceStateTable” content=“eltOnly”model=“closed”> <element type=“stateVariable” minOccurs=“1”maxOccurs=“*” /> </ElementType> <ElementType name=“relatedStateVariable”content=“textOnly” dt:type=“string” /> <ElementType name=“argument”content=“eltOnly” model=“closed”> <element type=“name” /> <elementtype=“relatedStateVariable” /> </ElementType> <ElementTypename=“argumentList” content=“eltOnly” model=“closed”> <elementtype=“argument” minOccurs=“1” maxOccurs=“*” /> </ElementType><ElementType name=“action” content=“eltOnly” model=“closed”> <elementtype=“name” /> <element type=“argumentList” minOccurs=“0” maxOccurs=“*”/> </ElementType> <ElementType name=“actionList” content=“eltOnly”model=“closed”> <element type=“action” minOccurs=“0” maxOccurs=“*” /></ElementType> <ElementType name=“scpd” content=“eltOnly”model=“closed”> <element type=“serviceStateTable” /> <elementtype=“actionList” /> </ElementType> </Schema>attribute

References an attribute in the new, derived language for the purposes ofdeclaring in which elements it may appear. Like any XML element, theAttributeType element may have attributes of its own. Using the requiredattribute within this element indicates whether the attribute ispresent; optional attributes have required=no.

AttributeType

Defines an attribute in the new, derived language. Like any XML element,the AttributeType element may have attributes of its own. Using the nameattribute within this element defines the name of the attribute as itwill be used in the derived language.

element

References an element for the purposes of declaring nesting. minOccursattribute defines minimum number of times the element occurs; default isminOccurs=1; optional elements have minOccurs=0. maxOccurs attributedefines maximum number of times the element occurs; default ismaxOccurs=1; elements that can appear one or more times havemaxOccurs=*.

ElementType

Defines an element in the new, derived language. name attribute defineselement name. dt:type attribute defines the data type for the value ofelement in the new, derived language. model attribute indicates whetherelements in the new, derived language can contain elements notexplicitly specified here; when only previously specific elements may beused, model=closed. content attribute indicates what content maycontain; elements that contain only other elements have content=eltOnly;elements that contain only strings have content=textOnly.

group

Organizes content into a group to specify a sequence. minOccursattribute defines minimum number of times the group occurs. maxOccursattribute defines maximum number of times the group occurs. orderattribute constrains the sequence of elements; when at most one elementis allowed, order=one.

3.4 Control: Augmenting the UPnP Template Language

As is the case with describing devices, some properties of services aredifficult to capture in the XML Schema formalism. For services inparticular, it is useful to describe the effect actions have on statevariables. This procedural information is awkward to describe in adeclarative language like XML, so below is a recommended vocabulary forUPnP Forum working committees to use when defining service actions orfor UPnP vendors to use when they wish to document the effects of extraactions.

ASSIGN (v, a)

Variable v becomes the value of argument a, i.e., v=a. v and a is thesame data type. <why both this and SET?>

DECREMENT (v)

Equivalent to INCREMENT (v) with allowedValueRange step treated as−step.

DECREMENT_BOUNDED (v)

Equivalent to INCREMENT_BOUNDED (v) with allowedValueRange step treatedas −step.

DECREMENT_WRAP (v)

Equivalent to INCREMENT_WRAP (v) with allowedValueRange step treated as−step.

INCREMENT (v)

Variable v becomes the value of v plus allowedValueRange step, i.e.,v=v+step. Equivalent to DECREMENT (v) with allowedValueRange steptreated as −step. v is either i4 or r8 and has an allowedValueRangedefinition.

INCREMENT_BOUNDED (v)

Variable v becomes the value of v plus allowedValueRange step, i.e.,v=v+step.

If step is greater than 0 and if v plus step would be greater thanallowedValueRange maximum, then v becomes maximum.

If step is less than 0 and if v plus step would be less thanallowedValueRange minimum, then v becomes minimum.

Equivalent to DECREMENT_BOUNDED (v) with allowedValueRange step treatedas −step. v is either i4 or r8 and has an allowedValueRange definition.

INCREMENT_WRAP (v, c)

Variable v becomes the value of v plus allowedValueRange step, i.e.,v=v+step.

If step is greater than 0, and if v plus step would be greater thanallowedValueRange maximum, then v becomes minimum plus step minus 1,i.e., v=minimum+step−1; if step is 1, this simplifies to v=minimum.

If step is less than 0 and if v plus step would be less thanallowedValueRange minimum, then v becomes maximum plus step plus 1,i.e., v=maximum+step+1; if step is −1, this simplifies to v=maximum.

Equivalent to DECREMENT_WRAP (v) with allowedValueRange step treated as−step. v is either i4 or r8 and has an allowedValueRange definition.

NEXT_STRING_BOUNDED (v)

Variable v becomes the next allowedValue after the current value of v.If v was already the last allowedValue, then v does not change. v is astring data type and has an allowedValueList definition.

NEXT_STRING_WRAP (v)

Variable v becomes the next allowedValue after the current value of v.If v was already the last allowedValue, then v becomes the firstallowedValue. v is a string data type and has an allowedValueListdefinition.

PREV_STRING_BOUNDED (v)

Variable v becomes the previous allowedValue before the current value ofv. If v was already the first allowedValue, then v does not change. v isa string data type and has an allowedValueList definition.

PREV_STRING_WRAP (v)

Variable v becomes the previous allowedValue before the current value ofv. If v was already the first allowedValue, then v becomes the lastallowedValue. v is a string data type and has an allowedValueListdefinition.

SET (v, c)

Variable v becomes the value of constant c, i.e., v=c. v and c is thesame data type.

TOGGLE (v)

-   -   Variable v becomes the boolean negation of the value of v, i.e.,        v=NOT v. v is boolean.        3.5 Control: Retrieving a Service Description

As explained above, after a control point has discovered a device andhas retrieved a device description, it may need to learn more about theservices provided by the device. Nearly identical to the process forretrieving a device description, a control point may retrieve a servicedescription using a description URL in the description (vs. discovery)message. (For details on retrieving a service description, pleaseconsult the corresponding discussion on retrieving a device descriptionin the section on Description.)

3.6 Control: Sending an Action

To send actions and receive confirmation, control points (and devices)use the following subset of the overall UPnP protocol stack. (Theoverall UPnP protocol stack is listed at the beginning of thisdocument.)

At the highest layer, control and query messages contain vendor-specificinformation, e.g., URL for control and argument values. Moving down thestack, vendor content is supplemented by information from a UPnP Forumworking committee, e.g., service types, action names, argument names.Messages from the layers above are hosted in UPnP-specific protocols,defined in this document. In turn, the above messages are formattedusing a Simple Object Access Protocol (SOAP) header and body elements,and the messages are delivered via HTTP over TCP over IP. For reference,colors in [square brackets] above indicate which protocol definesspecific header elements in the subscription messages listed below.

3.6.1 Control: Messages: Request

The Simple Object Access Protocol (SOAP) defines the use of XML and HTTPfor remote procedure calls. UPnP uses SOAP to deliver control messagesto devices and return acknowledgement or failure codes back to controlpoints.

SOAP defines additional HTTP headers, and to ensure that these are notconfused with other HTTP extensions, SOAP follows the HTTP ExtensionFramework and specifies a SOAP-unique URI in the MAN header and prefixesthe HTTP method with M-. In this case, the method is M-POST. UsingM-POST requires the HTTP server to find and understand the SOAP-uniqueURI and SOAP-specific headers.

To provide firewalls and proxies greater administrative flexibility,SOAP specifies that requests first be attempted without the MAN headeror M-prefix. If the request is rejected with a response of “405 MethodNot Allowed”, then a second request is sent using the MAN header andM-prefix. If that request is rejected with a response of “501 NotImplemented” or “510 Not Extended”, the request fails. (Other HTTPresponses is processed according to the HTTP specification.)

Below is a listing of a control message sent using the POST method(without the MAN header) followed by an explanation of the headers andbody. This is immediately followed by a listing of a control messagesent using the M-POST method and MAN header.

As explained above, a control message may include an key to indicatewhether the control point has received the most recent message. Toinclude a key, the body of a control message includes two SOAP headers,one for the event subscription UUID, and one for the key itself. Bothare illustrated in the listings below. The section on Eventing explainsthe contents of the two headers in detail.

To send a requested action to a device, a control point sends a requestwith method POST in the following format. Values in italics areplaceholders for actual values. POST path of control URL HTTP/1.1 HOST:host of control URL:port of control URL CONTENT-LENGTH: bytes in bodyCONTENT-TYPE: text/xml SOAPMETHODNAME: urn:schemas-upnp-org:service:serviceType:serviceVersion#actionName <SOAP:Envelopexmlns:SOAP=“urn:schemas-xmlsoap-org:soap.v1”> <SOAP:Header> <s:SIDxmlns:s=“urn:schemas-upnp-org:control:1:0”>subscriber UUID </s:SID><s:SequenceNumber>last event number</s:SequenceNumber> </SOAP:Header><SOAP:Body> <m:actionName xmlns:m=“urn:schemas-upnp-org:service:serviceType:serviceVersion”> <argumentName>argumentvalue</argumentName> </m:actionName> </SOAP:Body> </SOAP:Envelope>

Listed below are details for the request line, headers, and bodyelements appearing in the listing above. All header values and elementnames are case sensitive; values are not case sensitive except wherenoted. Except where noted, the order of elements is insignificant.

Request line

POST

Method defined by HTTP.

path control URL

Path component of URL for control for this service (controlURL subelement of service element of device description). Single, relative URL.

HTTP/1.1

HTTP version.

Headers

HOST

Domain name or IP address and optional port components of URL forcontrol for this service (controlURL sub element of service element ofdevice description). If the port is empty or not given, port 80 isassumed.

ACCEPT-LANGUAGE

(No ACCEPT-LANGUAGE header is used in control messages.)

CONTENT-LENGTH

Length of body in bytes. Integer.

CONTENT-TYPE

Is text/xlm.

MAN

(No MAN header in request with method POST.)

SOAPMETHODNAME

Starts with urn:schemas-upnp-org:service:, followed by UPnP standardservice type, colon, service version, hash mark, and name of action tobe invoked. If used in a request with method M-POST, header name isqualified with name space defined in MAN header. Single URI.

Body

SOAP:Envelope

xmlns namespace attribute is “urn:schemas-xmlsoap-org:soap.v1”. AllSOAP-defined elements is qualified with this namespace. Contains thefollowing sub elements:

SOAP:Header

Is qualified with SOAP namespace. Contains the following sub elements:

SID

Subscription Identifier. Unique identifier for this event subscription.(cf. section on Eventing.) xmlns namespace attribute isurn:schemas-upnp-org:control:1:0. Single URI.

SequenceNumber

Most recent event key received by control point from service. (cf.section on Eventing.) Is qualified with SID namespace. Single integer.

SOAP:Body

Is qualified with SOAP namespace. Contains the following sub element:

actionName

Name of element is name of action control point is requesting service toperform. xmlns namespace attribute starts withurn:schemas-upnp-org:service:, followed by UPnP standard service type,colon, and service version. Contains the following, ordered subelement(s):

argumentName

Repeat once for each argument. Value to be passed to action. (Elementname not qualified by a namespace; element nesting context issufficient.) Single data type as defined by UPnP Service Template.

If a request with POST is rejected with a response of “405 Method NotAllowed”, then a control point sends a second request with method M-POSTand MAN in the following format. Values in italics are placeholders foractual values.

M-POST path of control URL HTTP/1.1

HOST: host of control URL:port of control URL

CONTENT-LENGTH: bytes in body

CONTENT-TYPE: text/xml

MAN: “urn:schemas-xmlsoap-org:soap.v1”; ns=01

01-SOAPMETHODNAME:urn:schemas-upnp-org:service:serviceType:serviceVersion#actionName

(Message body for request with method M-POST is the same as body forrequest with method POST. See above.)

Request line

M-POST

Method defined by HTTP Extension Framework.

path of control URL

Path component of URL for control for this service (controlURL subelement of service element of device description). Single, relative URL.

HTTP/1.1

HTTP version.

Headers

HOST

Domain name or IP address and optional port components of URL forcontrol for this service (controlURL sub element of service element ofdevice description). If the port is empty or not given, port 80 isassumed.

ACCEPT-LANGUAGE

(No ACCEPT-LANGUAGE header is used in control messages.)

CONTENT-LENGTH

Length of body in bytes. Integer.

CONTENT-TYPE

Is text/xlm.

MAN

Is “urn:schemas-xmlsoap-org:soap.v1”. ns directive defines namespace(e.g., 01) for other SOAP headers (e.g., SOAPMETHODNAME).

SOAPMETHODNAME

-   -   Starts with urn:schemas-upnp-org:service:, followed by UPnP        standard service type, colon, service version, hash mark, and        name of action to be invoked. If used in a request with method        M-POST, header name is qualified with name space defined in MAN        header. Single URI.        3.6.2 Control: Messages: Response

If a service accepts an action request from a control point, the servicesends a response in the following format. Values in italics areplaceholders for actual values. HTTP/1.1 200 OK CONTENT-LENGTH: bytes inbody CONTENT-TYPE: text/xml DATE: when response was generated EXT:SERVER: OS / version, UPnP / 1.0,product / version <SOAP:Envelopexmlns:SOAP=“urn:schemas-xmlsoap-org:soap.v1”> <SOAP:Body><m:actionNameResponse xmlns:m=“urn:schemas-upnp-org:service:sType:sVers”> <return>return code</return></m:actionNameResponse> </SOAP:Body> </SOAP:Envelope>

Listed below are details for each of the headers and body elementsappearing in the listing above. All header values and element names arecase sensitive; values are not case sensitive except where noted. Exceptwhere noted, the order of elements is insignificant.

Headers

ACCEPT-LANGUAGE

(No ACCEPT-LANGUAGE header is used in control messages.)

CONTENT-LENGTH

Length of body in bytes. Integer.

CONTENT-TYPE

Is text/xlm.

DATE

When response was generated. RFC 1123 date.

EXT

Confirms that the MAN header was understood. (Header only; no value.)

SERVER

Concatenation of OS name, forward slash, OS version, comma, UPnP/1.0,comma, product name, forward slash, and product version. String.

Body

SOAP:Envelope

xmlns namespace attribute is “urn:schemas-xmlsoap-org:soap.v1”. AllSOAP-defined elements is qualified with this namespace. Contains thefollowing sub elements:

SOAP:Header

(No SOAP:Header element in response to control message.)

SOAP:Body

Is qualified with SOAP namespace. Contains the following sub element:

actionNameResponse

Name of element is action name prepended to Response. xmlns namespaceattribute starts with urn:schemas-upnp-org:service:, followed by UPnPstandard service type, colon, and service version. Contains thefollowing sub element:

return

(Element name not qualified by a namespace; element nesting context issufficient.) Has one of the following values:

0

Service accepts action request and will attempt to perform it. Legalonly from services without eventing.

1

Event key is valid. Service accepts action request and will attempt toperform it. Legal only from services with eventing.

If the service does not accept an action request from a control point,the service sends a response in the following format. Values in italicsare placeholders for actual values. HTTP/1.1 200 OK CONTENT-LENGTH:bytes in body CONTENT-TYPE: text/xml DATE: when response was generatedEXT: SERVER: OS / version, UPnP / 1.0,product / version <SOAP:Envelopexmlns:SOAP=“urn:schemas-xmlsoap-org:soap.v1”> <SOAP:Body> <SOAP:fault><faultcode>code for request error</faultcode> <faultstring>stringdescribing request error</faultstring> <runcode>did request get todevice?</runcode> </SOAP:fault> </SOAP:Body> </SOAP:Envelope>

(Headers for a response when a service does not accept an action requestare the same as headers for a response when a service does. See above.)

Body

SOAP:Envelope

xmlns namespace attribute is “urn:schemas-xmlsoap-org:soap.v1”. AllSOAP-defined elements is qualified with this namespace. Contains thefollowing sub elements:

SOAP:Header

(No Header element in response to control message.)

SOAP:Body

Is qualified with SOAP namespace. Contains the following sub element:

SOAP:fault

Why the service did not accept the action request. Contains thefollowing sub elements:

faultcode

Code identifying why service did not accept the action request. Has oneof the following values:

301

Invalid action name, i.e., no action by that name at this service.

302

Invalid arguments. Could be any of the following: not enough arguments,too many arguments, no argument by that name, one or more arguments areof the wrong data type.

303

Out of synchronization. Action request accompanied by invalid event key.

401

Action request failed. May be returned if current state of serviceprevents performing action. (No guarantee that service will return afault in such situations.)

faultstring

Short description for end user. Defined by a UPnP Forum workingcommittee or delegated to UPnP vendor. String. Recommend<256 characters.

runcode

Whether or not the request reached the service. Could be relevant ifanother system is operating as a proxy, bridge, or gateway for deviceand it's services. Is one of the following values:

0

Maybe

1

No

2

Yes

3.7 Control: Query for Variable

In addition to sending requested actions to a service, control pointsmay also poll the service for the value of a state variable by sending aquery message. A query message may query only one state variable;multiple query messages is sent to query multiple state variables.

3.7.1 Control: Messages: Query

To query for the value of a state variable, a control point sends arequest in the following format. Values in italics are placeholders foractual values. POST path of control URL HTTP/1.1 HOST: host of controlURL:port of control URL CONTENT-LENGTH: bytes in body CONTENT-TYPE:text/xml SOAPMETHODNAME: urn:schemas-upnp-org:control:1:0#QueryStateVariable <SOAP:Envelopexmlns:SOAP=“urn:schemas-xmlsoap-org:soap.v1”> <SOAP:Body><m:QueryStateVariable xmlns:m=“urn:schemas-upnp-org:control:1:0”><m:varName>variableName</m:varName> </m:QueryStateVariable> </SOAP:Body></SOAP:Envelope>

Listed below are details for the request line, headers, and bodyelements appearing in the listing above. All header values and elementnames are case sensitive; values are not case sensitive except wherenoted. Except where noted, the order of elements is insignificant.

Request line

POST

Method defined by HTTP.

path of control URL

Path component of URL for control for this service (controlURL subelement of service element of device description). Single, relative URL.

HTTP/1.1

HTTP version.

Headers

HOST

Domain name or IP address and optional port components of URL forcontrol for this service (controlURL sub element of service element ofdevice description). If the port is empty or not given, port 80 isassumed.

ACCEPT-LANGUAGE

(No ACCEPT-LANGUAGE header is used in control messages.)

CONTENT-LENGTH

Length of body in bytes. Integer.

CONTENT-TYPE

Is text/xlm.

MAN

(No MAN header in request with method POST.)

SOAPMETHODNAME

Is urn:schemas-upnp-org:control:1:0#QueryStateVariable. If used in arequest with method M-POST, header name is qualified with name spacedefined in MAN header. Single URI.

Body

SOAP:Envelope

xmlns namespace attribute is “urn:schemas-xmlsoap-org:soap.v1”. AllSOAP-defined elements is qualified with this namespace. Contains thefollowing sub elements:

SOAP:Header

(No SOAP:Header is used to query the value of a variable.)

SOAP:Body

Is qualified with SOAP namespace. Contains the following sub element:

QueryStateVariable

Action name. xmlns namespace attribute isurn:schemas-upnp-org:control:1:0. Contains the following, ordered subelement(s):

varName

Variable name. Is qualified by QueryStateVariable namespace. Values isname of state variable to be queried. String.

If a request with POST is rejected with a response of “405 Method NotAllowed”, then a control point sends a second request with method M-POSTand MAN as explained above.

3.7.2 Control: Messages: Response

To answer a query for the value of a state variable, the service sends aresponse in the following format. Values in italics are placeholders foractual vaules. HTTP/1.1 200 OK CONTENT-LENGTH: bytes in bodyCONTENT-TYPE: text/xml DATE: when response was generated EXT: SERVER: OS/ version, UPnP / 1.0,product / version <SOAP:Envelopexmlns:SOAP=“urn:schemas-xmlsoap-org:soap.v1”> <SOAP:Body><m:QueryStateVariableResponse xmlns:m=“urn:schemas-upnp-org:control:1:0”> <return>variable value</return></m:QueryStateVariableResponse> </SOAP:Body> </SOAP:Envelope>

Listed below are details for each of the headers and body elementsappearing in the listing above. All header values and element names arecase sensitive; values are not case sensitive except where noted. Exceptwhere noted, the order of elements is insignificant.

Headers

ACCEPT-LANGUAGE

(No ACCEPT-LANGUAGE header is used in control messages.)

CONTENT-LENGTH

Length of body in bytes. Integer.

CONTENT-TYPE

Is text/xlm.

DATE

When response was generated. RFC 1123 date.

EXT

Confirms that the MAN header was understood. (Header only; no value.)

SERVER

Concatenation of OS name, forward slash, OS version, comma, UPnP/1.0,comma, product name, forward slash, and product version. String.

Body

SOAP:Envelope

xmlns namespace attribute is “urn:schemas-xmlsoap-org:soap.v1”. AllSOAP-defined elements is qualified with this namespace. Contains thefollowing sub elements:

SOAP:Header

(No SOAP:Header is used to query the value of a variable.)

SOAP:Body

Is qualified with SOAP namespace. Contains the following sub element:

QueryStateVariableResponse

xmlns namespace attribute is urn:schemas-upnp-org:control:1:0. Containsthe following sub element:

return

(Element name not qualified by a namespace; element nesting context issufficient.) Value is current value of the state variable specified invarName element in request.

If the service cannot provide a value for the request, then the servicesends a response in the following format. Values in italics areplaceholders for actual values. HTTP/1.1 200 OK CONTENT-LENGTH: bytes inbody CONTENT-TYPE: text/xml DATE: when response was generated EXT:SERVER: OS / version, UPnP / 1.0,product / version <SOAP:Envelopexmlns:SOAP=“urn:schemas-xmlsoap-org:soap.v1”> <SOAP:Body> <SOAP:fault><faultcode>code for request error</faultcode> <faultstring>stringdescribing request error</faultstring> <runcode>did request get todevice?</runcode> </SOAP:fault> </SOAP:Body> </SOAP:Envelope>

(Headers for a response when a service cannot provide a value are thesame as headers for a response when a service does. See above.)

Body

SOAP:Envelope

xmlns namespace attribute is “urn:schemas-xmlsoap-org:soap.v1”. AllSOAP-defined elements is qualified with this namespace. Contains thefollowing sub elements:

SOAP:Header

(No Header element in response to control message.)

SOAP:Body

Is qualified with SOAP namespace. Contains the following sub element:

SOAP:fault

Why the service did not accept the action request. Contains thefollowing sub elements:

faultcode

Code identifying why service did not accept the action request. Has oneof the following values:

304

Invalid variable name, i.e., no state variable by that name at thisservice.

faultstring

Short description for end user. Defined by a UPnP Forum workingcommittee or delegated to UPnP vendor. String. Recommend<256 characters.

runcode

Whether or not the request reached the service. Could be relevant ifanother system is operating as a proxy, bridge, or gateway for deviceand it's services. Is one of the following values:

0

Maybe

1

No

2

Yes

4. Eventing

Eventing is Step 4 in UPnP networking. Eventing comes after discovery(Step 1) where control points find interesting device(s), and afterdescription (Step 2) where control points learn about devicecapabilities. Eventing is intimately linked with control (Step 3) wherecontrol points send actions to devices. Through eventing, control pointslisten to state changes in device(s). Control and eventing arecomplementary to presentation (Step 5) where control points display auser interface provided by device(s).

After a control point has (1) discovered a device and (2) retrieved adescription of the device, the control point has the bare essentials foreventing. As is the case with control, to learn more about the device'sservices, the control point retrieves a detailed UPnP description foreach service of interest.

As the section on Control explains, a UPnP description for a serviceincludes a list of actions the service responds to and a list ofvariables that model the state of the service at run time. If one ormore of these state variables are evented, then the service publishesupdates when these variables change, and a control point may subscribeto receive this information.

To subscribe to eventing, a control point sends a subscription message.If the subscription is accepted, the service responds with a durationfor the subscription. To keep the subscription active, a control pointrenews its subscription before the subscription expires. When a controlpoint no longer needs eventing from a particular service, the controlpoint cancels its subscription. This section explains subscription,renewal, and cancellation messages in detail below.

The service publishes changes to state variables by sending eventmessages. Event messages contain the names of one of more statevariables and the current value of those variables, expressed in XML. Aspecial initial event message is sent when a control point firstsubscribes; this event message contains the names and values for allevented variables and allows the subscriber to initialize its model ofthe state of the service. To support scenarios with multiple controlpoints, eventing is designed to keep all control points equally informedabout the effects of any action. Therefore, all subscribers are sent allevent messages, subscribers receive event messages for all eventedvariables (not just some), and event messages are sent no matter why thestate variable changed (either in response to a requested action orbecause the state the service is modeling changed). This sectionexplains the format of event messages in detail below.

Some state variables may change value too rapidly for eventing to beuseful. One alternative is to filter, or moderate, the number of eventmessages sent due to changes in a variable's value. Some state variablesmay contain values too large for eventing to be useful; for this, orother reasons, a service may designate one or more state variables asnon evented and never send event messages to a subscriber. To determinethe current value for such non-evented variables, control points pollthe service explicitly. This section explains how variable eventing isdescribed within a service description. The section on Control explainshow to poll a service for a variable value.

To prevent a race condition between events headed for control points andrequested actions headed for a service, control messages may include akey. With each new event message a service generates, the serviceincrements the key, and includes that key in the event message. When acontrol point sends a control message, it may choose to include a key.If a control message includes a key, the service checks to see if thekey is current, i.e., if no events have been sent since this key wasissued. If the key is current (or if there was no key in the controlmessage), then the service acknowledges the action request. If the keyis not current, the service fails the action request. This sectionexplains details of event keys and the synchronization between controland event messages.

To send and receive subscription and event messages, control points andservices use the following subset of the overall UPnP protocol stack.(The overall UPnP protocol stack is listed at the beginning of thisdocument.)

At the highest layer, subscription and event messages containvendor-specific information like URLs for subscription and duration ofsubscriptions or specific variable values. Moving down the stack, vendorcontent is supplemented by information from a UPnP Forum workingcommittee, like service identifiers or variable names. Messages from thelayers above are hosted in UPnP-specific protocols, defined in thisdocument. In turn, the above messages are formatted using General EventNotification Architecture (GENA) headers, and the messages are deliveredvia HTTP over TCP over IP. For reference, colors in [square brackets]above indicate which protocol defines specific header elements in thesubscription messages listed below.

The remainder of this section first explains subscription, includingdetails of subscription messages, renewal messages, and cancellationmessages. Second, it explains in detail how event messages are formattedand sent to control points, the initial event message, and how eventkeys synchronize control and eventing. Finally, it explains the UPnPTemplate Language as it pertains to eventing.

4.1 Eventing: Subscription

A service has eventing if and only if one or more of the state variablesare evented. If a service has eventing, it publishes event messages tointerested control points, or subscribers. The service maintains a listof subscribers, keeping for each subscriber the following information.

unique subscription identifier

-   -   Is unique over the lifetime of the subscription, however long or        short that may be. Generated by service in response to        subscription message. Recommend universally-unique identifiers        to ensure uniqueness. Single URI.        delivery URL for event messages

Provided by control point in subscription message. Single URL.

event key

Key is 0 for initial event message. Key is sequentially numbered foreach subsequent event message; control points can verify that no eventmessages have been lost if the control point has received sequentiallynumbered event keys. Single integer.

subscription duration

Amount of time, or duration until subscription expires. Single integeror keyword infinite.

The service may wish to persist subscriptions across power failures.While control points can recover from complete network failure, if theproblem is brief and localized to the device, reusing storedsubscriptions may speed recovery.

The list of subscribers is updated via subscription, renewal, andcancellation messages explained below and event messages explained laterin this section.

To subscribe to eventing for a service, a control point sends asubscription message containing a URL for the publisher, a serviceidentifier for the publisher, and a delivery URL for event messages. Thesubscription message may also include a requested duration for thesubscription. The URL and service identifier for the publisher come froma description message. As the section on Description explains, adescription message contains a device description. A device descriptioncontains (among other things), for each service, an eventing URL (in theeventSubURL element) and a service identifier (in the serviceIdelement); these correspond to the URL and service identifier for thepublisher, respectively.

The subscription message is a request to receive all event messages. Nomechanism is provided to subscribe to event messages on avariable-by-variable basis. A subscriber is sent all event messages fromthe service. This is one factor to be considered when designing aservice.

If the subscription is accepted, the service responds with uniqueidentifier for this subscription and a duration for this subscription. Aduration is chosen that matches assumptions about how frequently devicesare removed from the network; if devices are removed every few minutes,then the duration is similarly short, allowing a service to rapidlydeprecate any expired subscribers; if devices are semi-permanent, thenthe duration is very long, minimizing the processing and trafficassociated with renewing subscriptions.

As soon as possible after the subscription is accepted, the service alsosends the first, or initial event message to the subscriber. Thismessage includes the names and current values for all evented variables.(The data type and range for each variable is described in a servicedescription. The section on Control explains this in more detail.)

To keep the subscription active, a control point renews its subscriptionbefore the subscription expires by sending a renewal message. Therenewal message is send to the same URL as the subscription message, butthe renewal message does not include a delivery URL for event messages;instead the renewal message includes the subscription identifier. Theresponse for a renewal message is the same as one for a subscriptionmessage.

If a subscription expires, the subscription identifier becomes invalid,and the service stops sending event messages to the control point andcan clean up its list of subscribers. If the control point tries to sendany message other than a subscription message, the service will rejectthe message because the subscription identifier is invalid. To sendcontrol messages to the service, the control point sends a subscriptionmessage and get a new subscription identifier.

When a control point no longer needs eventing from a particular service,the control point cancels its subscription. Canceling a subscriptiongenerally reduces service, control point, and network load. If a controlpoint is removed abruptly from the network, it might be impossible tosend a cancellation message. As a fallback, the subscription willeventually expire on its own unless renewed.

Below is an explanation of the specific format of requests, responses,and errors for subscription, renewal, and cancellation messages.

4.1.1 Eventing: Subscribing: SUBSCRIBE with NT and CALLBACK

For each service in a device, a description message contains an eventingURL (eventSubURL sub element of service element in the devicedescription) and the UPnP service identifier (serviceId sub element inservice element in device description). To subscribe to eventing for aparticular service, a subscription message is sent to that service'seventing URL. The message contains that service's identifier as well asa delivery URL for event messages. A subscription message may alsoinclude a requested subscription duration.

To subscribe to eventing for a service, a control point sends a requestwith method SUBSCRIBE and NT and CALLBACK headers in the followingformat. Values in italics are placeholders for actual values.

SUBSCRIBE publisher path HTTP/1.1

HOST: publisher host:publisher port

CALLBACK: <delivery URL>

NT: upnp:event

TIMEOUT: Second-requested subscription duration

(No body for request with method SUBSCRIBE.)

Listed below are details for the request line and headers appearing inthe listing above. All header values are case sensitive except wherenoted.

Request line

SUBSCRIBE

Method defined by GENA.

publisher path

Path component of eventing URL (eventSubURL sub element in serviceelement in device description). Single, relative URL.

HTTP/1.1

HTTP version.

Headers

HOST

Domain name or IP address and optional port components of eventing URL(eventSubURL sub element in service element in device description). Ifthe port is missing or empty, port 80 is assumed.

CALLBACK

Location to send event messages to. Defined by UPnP vendor. If there ismore than 1 URL, when the service sends events, it will try these URLsin order until one succeeds. One or more URLs separated by anglebrackets.

NT

Notification Type. Is upnp:event.

SID

(No SID header is used to subscribe.)

TIMEOUT

Requested duration until subscription expires, either number of secondsor infinite. Recommendation by a UPnP Forum working committee. Definedby UPnP vendor. Keyword Second—followed by an integer (no space) orkeyword infinite.

To accept the subscription, the service assigns a unique identifier forthe subscription, assigns a duration for the subscription, and sends aninitial event message (explained in detail later in this section). Toaccept a subscription request, a service sends a response in thefollowing format. Values in italics are placeholders for actual values.

HTTP/1.1 200 OK

DATE: when response was generated

SERVER: OS/version, UPnP/1.0, product/version

SID: uuid:subscription UUID

TIMEOUT: Second-actual subscription duration

(No body for response to a request with method SUBSCRIBE.)

Listed below are details for headers appearing in the listing above. Allheader values are case sensitive except where noted.

Headers

DATE

When response was generated. RFC 1123 date.

SERVER

Concatenation of OS name, forward slash, OS version, comma, UPnP/1.0,comma, product name, forward slash, and product version. String.

SID

Subscription identifier. Is universally-unique. Begins with uuid:.Defined by UPnP vendor. Single URI.

TIMEOUT

Actual duration until subscription expires, either number of seconds orinfinite. Recommendation by a UPnP Forum working committee. Defined byUPnP vendor. Is >1800 seconds (30 minutes). Keyword Second—followed byan integer (no space) or keyword infinite.

If a service cannot accept another event subscriber, or if there is anerror with the subscription request, the service sends a response withone of the following errors.

Errors

Incompatible headers

400 Bad Request. If SID header and one of NT or CALLBACK headers arepresent, the service responds with HTTP error 400 Bad Request.

Missing or invalid CALLBACK

412 Precondition Failed. If CALLBACK header is missing or does notcontain a valid HTTP URL, the service responds with HTTP error 412Precondition Failed.

Unable to accept subscription

5xx. If a service is not able to accept a subscription, it responds witha HTTP 500-series error code.

Other errors may be returned by layers in the protocol stack below UPnP.Consult documentation on those protocols for details.

4.1.2 Eventing: Renewing a Subscription: SUBSCRIBE with SID

To renew a subscription to eventing for a particular service, a renewalmessages is sent to that service's eventing URL. However, unlike aninitial subscription message, a renewal message does not contain eitherthe service's identifier nor a delivery URL for event messages. Instead,the message contains the subscription identifier assigned by theservice, providing an unambiguous reference to the subscription to berenewed. Like a subscription message, a renewal message may also includea requested subscription duration.

The renewal message uses the same method as the subscription message,but the two messages use a disjoint set of headers; renewal uses SID andsubscription uses NT and CALLBACK. A message that includes SID andeither of NT or CALLBACK headers is an error.

To renew a subscription to eventing for a service, a control point sendsa request with method SUBSCRIBE and SID header in the following format.Values in italics are placeholders for actual values.

SUBSCRIBE publisher path HTTP/1.1

HOST: publisher host:publisher port

SID: uuid:subscription UUID

TIMEOUT: Second-requested subscription duration

(No body for method with request SUBSCRIBE.)

Listed below are details for the request line and headers appearing inthe listing above. All header values are case sensitive except wherenoted.

Request line

SUBSCRIBE

Method defined by GENA.

publisher path

Path component of eventing URL (eventSubURL sub element in serviceelement in device description). Single, relative URL.

HTTP/1.1

HTTP version.

Headers

HOST

Domain name or IP address and optional port components of eventing URL(eventSubURL sub element in service element in device description). Ifthe port is missing or empty, port 80 is assumed.

CALLBACK

(No CALLBACK header is used to renew an event subscription.)

NT

(No NT header is used to renew an event subscription.)

SID

Subscription identifier. Is the subscription identifier assigned byservice in response to subscription request. Is universally-unique.Begins with uuid:. Defined by UPnP vendor. Single URI.

TIMEOUT

Requested duration until subscription expires, either number of secondsor infinite. Recommendation by a UPnP Forum working committee. Definedby UPnP vendor. Keyword Second—followed by an integer (no space) orkeyword infinite.

To accept a renewal, the service reassigns a duration for thesubscription. (No initial event message. See below.) To accept arenewal, a service sends a response in the same format as a response toa request for a new subscription.

If a service cannot accept the renewal, or if there is an error with therenewal request, the service sends a response with one of the followingerrors.

Errors

Incompatible headers

400 Bad Request. If SID header and one of NT or CALLBACK headers arepresent, the service responds with HTTP error 400 Bad Request.

Invalid SID

404 Not Found. If a SID does not correspond to a known, un-expiredsubscription, the service responds with HTTP error 404 Not Found.

Missing SID

412 Precondition Failed. If the SID header is missing or empty, theservice responds with HTTP error 412 Precondition Failed.

Unable to accept renewal

5xx. If the service is not able to accept a renewal, it responds with aHTTP 500-series error code.

Other errors may be returned by layers in the protocol stack below UPnP.Consult documentation on those protocols for details.

4.1.3 Eventing: Canceling a Subscription: UNSUBSCRIBE

When eventing is no longer needed from a particular service, acancellation message is sent to that service's eventing URL. The messagecontains the subscription identifier. Canceling a subscription generallyreduces service, control point, and network load. If a control point isremoved abruptly from the network, it might be impossible to send acancellation message. As a fallback, the subscription will eventuallyexpire on its own unless renewed.

To cancel a subscription to eventing for a service, a control pointsends a request with method UNSUBSCRIBE in the following format. Valuesin italics are placeholders for actual values.

UNSUBSCRIBE publisher path HTTP/1.1

HOST: publisher host:publisher port

SID: uuid:subscription UUID

(No body for request with method UNSUBSCRIBE.)

Listed below are details for the request line and headers appearing inthe listing above. All header values are case sensitive except wherenoted.

Request line

UNSUBSCRIBE

Method defined by GENA.

publisher path

Path component of eventing URL (eventSubURL sub element in serviceelement in device description). Single, relative URL.

HTTP/1.1

HTTP version.

Headers

HOST

Domain name or IP address and optional port components of eventing URL(eventSubURL sub element in service element in device description). Ifthe port is missing or empty, port 80 is assumed.

CALLBACK

(No CALLBACK header is used to cancel an event subscription.)

NT

(No NT header is used to cancel an event subscription.)

SID

Subscription identifier. Is the subscription identifier assigned byservice in response to subscription request. Is universally-unique.Begins with uuid:. Defined by UPnP vendor. Single URI.

TIMEOUT

(No TIMEOUT header is used to cancel an event subscription.)

To cancel a subscription, a service sends a response in the followingformat. Values in italics are placeholders for actual values.

HTTP/1.1 200 OK

If there is an error with the cancellation request, the service sends aresponse with one of the following errors.

Errors

Incompatible headers

400 Bad Request. If SID header and one of NT or CALLBACK headers arepresent, the service responds with HTTP error 400 Bad Request.

Invalid SID

404 Not Found. If a SID does not correspond to a known, un-expiredsubscription, the service responds with HTTP error 404 Not Found.

Missing SID

412 Precondition Failed. If the SID header is missing or empty, theservice responds with HTTP error 412 Precondition Failed.

Other errors may be returned by layers in the protocol stack below UPnP.Consult documentation on those protocols for details.

4.2 Eventing: Event Messages

A service publishes changes to its state variables by sending eventmessages. These messages contain the names of one or more statevariables and the current value of those variables. Event messages issent as soon as possible to get accurate information about the serviceto control points and allow control points to display a responsive userinterface. If the value of more than one variable is changing at thesame time, the service bundles these changes into a single event messageto reduce processing and network traffic.

As explained above, an initial event message is sent when a controlpoint first subscribes; this event message contains the names and valuesfor all evented variables and allows the subscriber to initialize itsmodel of the state of the service. This message is sent as soon aspossible after the service accepts a subscription.

Event messages are tagged with an event key to detect a race conditionbetween event messages headed for control points and control messagesheaded for a device. A separate event key is maintained by the servicefor each subscription to facilitate error detection (as explainedbelow). The event key for a subscription is initialized to 0 when theservice sends the initial event message. For each subsequent eventmessage, the service increments the event key for a subscription, andincludes that updated key in the event message. Any implementation ofevent keys handles overflow and wrap the event key back to 1 (not 0).Control point also handles this special case when the next event key isnot an increment of the previous key.

If there is no response from a control point to the event message, theservice continues to send event messages to the control point until thesubscription expires.

To repair an event subscription, e.g., if a control point has missed oneor more event messages, a control point unsubscribes and re-subscribes.By doing so, the control point will get a new subscription identifier, anew initial event message, and a new event key. With these, the controlpoint can resume sending successful control messages to the service.

4.2.1 Eventing: Event Messages: NOTIFY

To send an event message, a service sends a request with method NOTIFYin the following format. Values in italics below are placeholders foractual values. NOTIFY delivery path HTTP/1.1 HOST: deliveryhost:delivery port CONTENT-TYPE: text/xml CONTENT-LENGTH: bytes in bodyNT: upnp:event NTS: upnp:propchange SID: uuid:subscription UUID SEQ:event key <e:propertyset xmlns:e=“urn:schemas-upnp-org:event:1:0”><e:property> <variableName>new value<variableName> </e:property> Othervariable names and values (if any) go here. </e:propertyset>

Listed below are details for the request line, headers, and bodyelements appearing in the listing above. All header values are casesensitive except where noted. All body elements and attributes are casesensitive; body values are not case sensitive except where noted. Exceptwhere noted, the order of elements is insignificant.

Request line

NOTIFY

Method defined by GENA.

delivery path

Path component of delivery URL (CALLBACK header in subscriptionmessage). Destination for event message. Single, relative URL.

HTTP/1.1

HTTP version.

Headers

HOST

Domain name or IP address and optional port components of delivery URL(CALLBACK header in subscription message). If the port is missing orempty, port 80 is assumed.

CONTENT-LENGTH

Length of body in bytes. Integer.

CONTENT-TYPE

Is text/xml.

NT

Notification Type. Is upnp:event.

NTS

Notification Sub Type. Is upnp:propchange.

SID

Subscription identifier. Is universally unique. Begins with uuid:.Defined by UPnP vendor. Single URI.

SEQ

Event key. Is 0 for initial event message. Is incremented by 1 for eachevent message sent to a particular subscriber. Is 8 bytes. Singleinteger.

Body

propertyset

xmlns namespace attribute is urn:schemas-upnp-org:event:1:0. All subelements is qualified with this namespace. Contains the following subelement.

property

Repeat once for each variable name and value in the event message. Isqualified by propertyset namespace. Contains the following sub element.

variableName

Element is name of a state variable that changed (name sub element ofstateVariable element in service description). Is qualified bypropertyset namespace. Values is the new value for this state variable.Single data type as specified by UPnP Service Template.

For future extensibility, when processing XML like the listing above,devices and control points ignore any unknown elements and any subelements or content as specified by the Flexible XML Processing Profile(FXPP).

To acknowledge receipt of this event message, a control point respondsin the following format.

HTTP/1.1 200 OK

(No body for a request with method NOTIFY.)

If there is an error with the event message, the control point respondswith one of the following errors.

Errors

Missing SID

412 Precondition Failed. If the SID header is missing or empty, thecontrol point responds with HTTP error 412 Precondition Failed.

Invalid SID

412 Precondition Failed. If a SID does not correspond to a knownsubscription, the control point responds with HTTP error 412Precondition Failed. (Service terminates this SID when it receives thiserror response.)

Missing NT or NTS header

400 Bad Request. If the NT or NTS header is missing, the control pointresponds with HTTP error 400 Bad Request.

Invalid NT or NTS header

(200 OK. No error. If NT or NTS header is invalid, the control pointignores it and respond with HTTP 200 OK.)

Other errors may be returned by layers in the protocol stack below UPnP.Consult documentation on those protocols for details.

4.3 Eventing: UPnP Template Language for Eventing

The UPnP Template Language defines well-formed templates for devices andservices. To a lesser extent, it also provides a template for the bodyof event messages. The section on Description explains the UPnP TemplateLanguage as it pertains to devices, and the section on Control explainsthe UPnP Template Language as it pertains to services. As explained inthose sections, the UPnP Template Language is written in XML syntax andis derived from XML Schema (Part 1: Structures, Part 2: Datatypes).Below is a listing of this language as it pertains to eventing. Theelements it defines are used in event messages; they are colored greenhere, and they are colored green in the listing above. Below is wherethese elements are defined (though it is a minimal definition); above iswhere they are used.

Immediately following this is a brief explanation of the XML Schemaelements, attributes, and values used. The reference to XML Schema atthe end of this section has further details.

UPnP Template Language for Eventing <?xml version=“1.0” ?> <Schemaname=“urn:schemas-upnp-org:event:1:0”xmlns=“urn:schemas-microsoft-com:xml-data”xmlns:dt=“urn:schemas-microsoft-com:datatypes”> <ElementTypename=“propertyset” content=“eltOnly”> <element type=“property”maxOccurs=“*” /> </ElementType> <ElementType name=“property”content=“eltOnly” model=“open” /> </Schema>element

References an element for the purposes of declaring nesting. maxOccursattribute defines maximum number of times the element occurs; default ismaxOccurs=1; elements that can appear one or more times havemaxOccurs=*.

ElementType

Defines an element in the new, derived language. name attribute defineselement name. model attribute indicates whether elements in the new,derived language can contain elements not explicitly specified here;when only unspecified sub elements may be included, model=open. contentattribute indicates what content may contain; elements that contain onlyother elements have content=eltOnly.

As explained in the section on Control, the UPnP Template Language forservices also specifies a sendEvents attribute for a state variable. Thedefault value for this attribute is yes. To denote that a state variableis evented, the value of this attribute is yes (or the attribute isomitted) in a service description; to denote that a state variable isnon-evented, the value is no. Note that if all of a service's statevariables are non-evented, the service has nothing to publish, andcontrol points cannot subscribe and will not receive event messages fromthe service.

4.4 Eventing: Augmenting the UPnP Template Language

It is useful to augment the description of devices and services withannotations that are not captured in the UPnP Template Language. To alesser extent, there is value in these annotations to capture eventfiltering, or moderation.

As explained above, some state variables may change value too rapidlyfor eventing to be useful. Below is a recommended vocabulary for UPnPForum working committees or UPnP vendors to document moderation in thenumber of event messages sent due to changes in a variables value.

maximumRate=n

Optional. State variable v will not be part of an event message moreoften than n seconds. If v is the only variable changing, then an eventmessage will not be generated more often than every n seconds. If vceases to change after an event message has been sent but before nseconds have transpired, an event message is sent with the new value ofv. Recommended for variables that model continuously changingproperties. Single integer.

minimumDelta=n

Optional. State variable v will not be part of an event message unlessits value has changed by more than n * allowedValueRange step since thelast time an event message was sent that included v, e.g., unless v hasbeen incremented n times. (cf. INCREMENT, INCREMENT_BOUNDED, andINCREMENT_WRAP explained in the section on Control.) Only definedvariables with number and real data type. Recommended for variables thatmodel counters. Single integer.

5. Presentation

Presentation is Step 5 in UPnP networking. Presentation comes afterdiscovery (Step 1) where control points find interesting device(s), andafter description (Step 2) where control points learn about devicecapabilities. Presentation exposes an HTML-based user interface forcontrolling and/or viewing device status. Presentation is complementaryto control (Step 3) where control points send actions to devices, andeventing (Step 4) where control points listen to state changes indevice(s).

After a control point has (1) discovered a device and (2) retrieved adescription of the device, the control point is ready to beginpresentation. If a device has a URL for presentation, then the controlpoint can retrieve a page from this URL, load the page into a browser,and depending on the capabilities of the page, allow a user to controlthe device and/or view device status. The degree to which each of thesecan be accomplished depends on the specific capabilities of thepresentation page and device.

The URL for presentation is contained within the presentationURL elementin the device description. The device description is delivered via adescription message. The section on Description explains the devicedescription and description messages in detail.

Retrieving a presentation page is a simple HTTP-based process and usesthe following subset of the overall UPnP protocol stack. (The overallUPnP protocol stack is listed at the beginning of this document.)

At the highest layer, the presentation page is specified by a UPnPvendor. Moving down the stack, the UPnP Device Architecture specifiesthat this page be written in HTML. The page is delivered via HTTP overTCP over IP. For reference, colors in [square brackets] are included forconsistency with other sections in this document.

To retrieve a presentation page, the control point issues an HTTP GETrequest to the presentation URL, and the device returns a presentationpage.

Unlike the UPnP Device and Service Templates, and standard device andservice types, the capabilities of the presentation page are completelyspecified by the UPnP vendor. The presentation page is not under theauspices of a UPnP Forum working committee. The page is an HTML page; itis version HTML 3.0 or later. However, other design aspects are left tothe vendor to specify. This includes, but is not limited to, allcapabilities of the control point's browser, scripting language orbrowser plug-ins used, and means of interacting with the device. Toimplement a presentation page, a UPnP vendor may wish to use UPnPmechanisms for control and/or eventing, leveraging the device's existingcapabilities but is not constrained to do so.

Glossary

action

Command exposed by a service. Takes one or more arguments but does notreturn values. For more information, see section on Control.

argument

Parameter for action exposed by a service. For more information, seesection on Control.

control point

Retrieves device and service descriptions, sends actions to services,polls for service state variables, and receives events from services.

device

Logical device. A container. May embed other logical devices. Embeds oneor more services. For more information, see section on Description.

device definition

Formal definition of a logical device, expressed in the UPnP TemplateLanguage. Written in XML syntax. Specified by a UPnP vendor by fillingin the placeholders in a UPnP Device Template, including, e.g.,manufacturer name, model name, model number, serial number, and URLs forcontrol, eventing, and presentation. For more information, see sectionon Description.

device type

Standard device types are denoted by urn:schemas-upnp-org:device:followed by a unique name assigned by a UPnP Forum working committee.One-to-one relationship with UPnP Device Templates. UPnP vendors mayspecify additional device types; these are denoted byurn:domain-name:device: followed by a unique name assigned by thevendor, where domain-name is a domain name registered to the vendor. Formore information, see section on Description.

event

Notification of one or more changes in state variables exposed by aservice. For more information, see section on Eventing.

root device

A logical device that is not embedded in any other logical device. Formore information, see section on Description.

service

Logical functional unit. Exposes actions and models the state of aphysical device with state variables. For more information, see sectionon Control.

service definition

Formal definition of a logical service, expressed in the UPnP Templatelanguage. Written in XML syntax. Specified by a UPnP vendor by fillingin any placeholders in a UPnP Service Template. (Was SCPD.) For moreinformation, see section on Control.

service type

Standard service types are denoted by urn:schemas-upnp-org:service:followed by a unique name assigned by a UPnP forum working committee,colon, and a version number. One-to-one relationship with UPnP ServiceTemplates. UPnP vendors may specify additional services; these aredenoted by urn:domain-name:service: followed by a unique name assignedby the vendor, colon, and a version number, where domain-name is adomain name registered to the vendor. For more information, see sectionon Description.

SOAP

Simple Object Access Protocol. A remote-procedure call mechanism basedon XML that sends commands and receives values over HTTP. For moreinformation, see section on Control.

SSDP

Simple Service Discovery Protocol. A multicast discovery and searchmechanism that uses a multicast variant of HTTP over UDP. For moreinformation, see section on Discovery.

state variable

Single facet of a model of a physical service. Exposed by a service. Hasa name, data type, optional default value, optional constraints values,and may trigger events when its value changes. For more information, seesection on Control.

UPnP Device Template

Template listing device type, embedded devices (if any), and services.Written in XML syntax and derived from the UPnP Template Language.Defined by a UPnP Forum working committee. One-to-one relationship withstandard device types. For more information, see section on Description.

UPnP Service Template

Template listing action names, parameters for those actions, statevariables, and properties of those state variables. Written in XMLsyntax and derived from the UPnP Template Language. Defined by a UPnPForum working committee. One-to-one relationship with standard servicetypes. For more information, see section on Control.

UPnP Template Language

Defines the elements and attributes used in UPnP Device and ServiceTemplates. Written in XML syntax and derived from XML Schema (Part 1:Structures, Part 2: Datatypes). Defined by the UPnP Device Architectureherein. For more information, see sections on Description and Control.

Having described and illustrated the principles of our invention withreference to an illustrated embodiment, it will be recognized that theillustrated embodiment can be modified in arrangement and detail withoutdeparting from such principles. It should be understood that theprograms, processes, or methods described herein are not related orlimited to any particular type of computer apparatus, unless indicatedotherwise. Various types of general purpose or specialized computerapparatus may be used with or perform operations in accordance with theteachings described herein. Elements of the illustrated embodiment shownin software may be implemented in hardware and vice versa.

In view of the many possible embodiments to which the principles of ourinvention may be applied, it should be recognized that the detailedembodiments are illustrative only and should not be taken as limitingthe scope of our invention. Rather, we claim as our invention all suchembodiments as may come within the scope and spirit of the followingclaims and equivalents thereto.

1. In a network of computing devices interoperating via a peernetworking protocol, a peer networking host system comprising: aprogramming interface supporting interaction with software for a logicaldevice having a set of device services; a discovery server operating torespond to discovery requests in the peer networking protocol receivedat the peer networking host system from computing devices on the networkthat seek discovery inclusive of the logical device; a descriptionserver operating to respond to requests from computing devices on thenetwork in the peer networking protocol for data descriptive of thelogical device; a control server operating to proxy service controlcommands from computing devices on the network in the peer networkingprotocol by invoking respective of the device services corresponding tothe service control commands; and an eventing server operatingresponsive to an event notification sourced from the software todistribute the event notification per the peer networking protocol tothose of the computing devices requesting to receive such notification.2. The peer networking host system of claim 1 wherein the applicationprogramming interface receives description data of the logical devicefrom the software.
 3. A computer-readable data carrying medium having alink-able program module thereon, the program module executable on acomputer in a network of computing devices interoperating via a peernetworking protocol to provide hosting of the peer networking protocolfor logical device software that operates as a logical device having aset of services on the computer, the program module comprising: adiscovery programming interface for receiving device discovery data fromthe logical device software; a discovery protocol server moduleoperating to serve discovery responses to discovery requests received inthe peer networking protocol at the computer from the network that seekdiscovery inclusive of the logical device; a description programminginterface for receiving device description data from the logical devicesoftware; a description protocol server module operating to servedescription responses to description requests received in the peernetworking protocol at the computer from the network and directed towardthe logical device; a service control programming interface forinterfacing to the services; a service control server module operatingresponsive to control messages received in the peer networking protocolat the computer from the network that are directed to the services ofthe logical device so as to invoke the services in accordance with thecontrol messages; an eventing programming interface for receiving eventnotifications from the logical device software; and an event servermodule operating to distribute event notifications in the peernetworking protocol to computing devices on the network that haverequested to receive such event notifications.